#speedster biology 101

[ikibli]

Speedster Biology 101: Teeth

Speedsters have a dentition system closer to a shark’s than a human’s.

They have a second row of sharper, slightly tilted and offset teeth that are normally hidden within the jaw, and extendable upper canines. This is mostly used to aid in eating tough, hard or slippery food, though they can be extended voluntarily, and do aid the combat effectiveness of the bite somewhat. The upper canines and secondary teeth extend involuntarily when angry or defensive.

When extended, this gives the appearance of a single row of vaguely serrated teeth with inch-long fangs. When retracted, their teeth are human-looking, though with unusually sharp and large upper canines.

Speedster teeth shed and regrow constantly- each primary tooth being replaced naturally once every four or five months, and each secondary tooth every two years, except for the upper canines, which are replaced only when broken. All teeth regrow fully in a few hours, assuming no other injuries, and teeth that get damaged will loosen and fall out after a few minutes, beginning to regrow almost immediately after.

This is the case for their entire lives- they don’t have baby teeth, though their teeth are naturally shed more often as children, and the premolars and wisdom teeth still aren’t present in their initial sets of teeth. Young speedsters will often have upper canines that are smaller proportionally than an adult’s, since the upper canines still only shed when broken.

 In order to break their teeth, speedsters will often chew on metal or stone objects or, when older, score marks on them to get them to fall out. This is perfectly normal and actually recommended, since minor damage like cavities, demineralization or discoloration doesn’t cause them to fall out unless the dentin is exposed and/or damaged.

Speedster teeth are structurally similar to human teeth, though they are easier to break.

[ikibli]

Speedster Biology 101: Unconsciousness

Speedsters sleep in short 5-10 minute increments scattered throughout the day, for about one and a half hours total per day. They tend to sleep lightly, waking if their speedsense detects a major anomaly nearby(like an explosion, gunshot or vehicle crash), and their dreams often contain large amounts of input from their speedsense and hearing.

Traumatic unconsciousness occurs only when their injuries are severe enough that keeping them conscious while they heal would be too taxing on their body, and they often take a long time to fall unconscious even after receiving those kinds of injuries- from a few seconds to several minutes.

This always includes injuries to both hearts simultaneously, injuries to one heart and two or more primary/secondary lungs simultaneously, non-superficial brain damage, the spinal cord being severed at the top-most thoracic vertebra or higher, major injuries to nearly every body part(AKA massive damage from explosions or crushing) or being cut in half. Airway constriction can also cause unconsciousness, but only because lack of oxygen eventually causes brain damage.

Decapitation is the closest to a guaranteed fatal wound short of complete disintegration, and even then they will still be alive for several minutes and conscious for several seconds(though it’s unlikely for the majority of medical treatment to be able to help).

Anything less than that will be painful and crippling, but they can still move anything still connected and stay conscious- though if there’s no pressing need to stay conscious with major(guaranteed to be permanently crippling on a human) injuries, they’ll fall unconscious to heal, even if their wounds aren’t severe enough to always necessitate that.

An unconscious speedster’s skin will pale and their flesh will cool as their metabolism slows and blood is pulled back towards their brain and vital organs. They’ll also stop holding their breath without refilling their air sacs if they were currently doing so.

The end result is that a speedster unconscious from traumatic injuries is easily mistaken as dead, especially since their pulse will still be unreadable if both of their hearts are functional(though not necessarily entirely intact).

An unconscious speedster will wake up in a variable amount of time ranging from a few hours for things like shattered bones or a severed limb(though severed limbs will still take two to three weeks to heal, they’ll just be conscious in the meantime), to several days for organ injuries, up to a month or two for being cut in half or mangled by an explosion.

This is assuming that the injuries that caused their unconsciousness are the only ones they have and they were left undisturbed somewhere non-hazardous- if they have numerous minor injuries as well, or they are left somewhere with a mild or moderate environmental hazard(like underground or somewhere with a dangerous ambient temperature), it might take longer.

Speedsters are very hard to kill or even incapacitate as a result of their healing factor, redundant biology, immunity to most toxins and the fact that their tissues are designed to repeatedly suffer minor tears and breaks and have minimal dependencies on other parts and tissues. This is entirely intentional- the Speed Force loves its children and also knows that they are idiots with no self-preservation instinct.

[ikibli]

Speedster Biology 101: Circulatory System

Speedsters have two hearts, both of which beat in alternation and much, much faster than a human’s, thus producing the illusion that they don’t have a pulse, since the periods where neither of their hearts are pumping blood are too short to produce any measurable arterial contraction or reduction in blood pressure.

Their heartbeats also sound more like mechanical humming than a human’s heartbeat, and each beat is quieter. As a result, people with super-hearing can often lose track of their heartbeats(much like their breathing) in background noise.

The primary heart is in roughly the same place as a human’s, and the secondary heart is slightly smaller, and positioned several inches lower down on the opposite side of the body. Both are basically human in anatomy, except for the differently placed vessels on the secondary heart.

They can live without one of their hearts, though if one is damaged or missing, they will tire much faster, have low blood pressure, can’t hold their breath or run at high speeds for as long and will have a somewhat readable if extremely fast pulse. Their heartbeat is still a hum due to its speed, though it sounds different.

As an essential organ, even a completely missing heart will regrow in 2-3 days and lesser wounds will heal in a few hours, assuming they don’t have any other major injuries that are actually life-threatening.

Speedster blood is much brighter than a human’s- still easily mistaken for normal blood by the vast majority of people, especially venous blood(which is only slightly brighter than normal arterial blood). This is because they have hemoglobin of a modified type that can store more oxygen, and more hemoglobin total- running at high speeds, even with new air constantly being piped in, needs very efficient oxygen delivery(which is why they have two hearts to pump blood faster).

The speedster circulatory system is designed to seal the punctured blood vessels in a wound (both through healing-factor enhanced clotting and involuntarily-controlled muscles in the walls of larger blood vessels designed to pinch them shut) a few seconds after an initial spurt of high-pressure blood. Even small, superficial wounds will produce a short spray that can travel some distance. 

Speedster blood is sweet-tasting and reads as severely hyperglycemic, since their tissues need high quantities of energy available at a moment's notice.

Speedsters replace lost blood very quickly- they basically can't die of blood loss and it's very hard to get them even light-headed unless it's being ripped out of their body by something supernatural or they're already anemic.

The secondary heart is not fully developed in young speedsters until age six, and before then, damage to the primary heart can be lethal or crippling. Speedsters younger than two will also bleed from major wounds for several minutes, since their vessel-sealing muscles are undeveloped.

[ikibli]

Speedster Biology 101: Senses

Vision

Speedsters don’t have backwards retinas, and thus don’t have a blind spot where the ocular nerve is.

They also have better perception of motion and better peripheral vision, as well as the ability to change the focus of their attention without moving their eyes. As a result, they tend to either turn their entire head to look at something with their central vision or not move their eyes at all and simply shift their attention to something in their peripheral vision.

Otherwise, their vision is human standard. 

They have nictitating membranes(which are under voluntary control), and their involuntary blinking is less frequent and uses the nictitating membranes instead of the upper and lower eyelids.

Their upper and lower eyelids can be closed and opened voluntarily, and fall shut automatically when asleep or unconscious.

The nictitating membrane closes reflexively when startled or something moves quickly near their eyes, much like a human’s blink reflex. It also closes when running, or when otherwise excited. (The Speed Force crossed a few wires- speedsters instinctively close their nictitating membranes and (when extremely emotional) start holding their breath when excited, scared, aroused or happy.)

Hearing and Speedsense

Speedsters’ hearing has been mashed into their speedsense- they interpret some motion as sound, and some sound as motion. It’s more acute and discriminatory than a human’s, but it’s only slightly above peak human. They can also hear ultrasonic and infrasonic sounds- much of speedtalk and their involuntary vocalizations is ultrasonic.

Their speedsense allows them to feel vibrations and (vaguely) air currents near them, as well as motion as a discrete concept without any carrier.

This allows them to judge speed and trajectory finely enough to dodge attacks they can’t see or identify people based on their gaits, and is closely linked enough with their proprioception that they can adjust their gait and stance both consciously(such as to mimic someone else) and unconsciously(such as to balance on a ledge or walk on a slippery surface).

The ear canals of speedsters have skin flaps that seal them shut when running, swimming or their hearing is overstimulated. Unlike the nictitating membranes, they only close involuntarily.

Smell and Taste

Speedsters do have a sense of taste, but they don’t have a sense of smell, since their nasal passages were redesigned to accommodate constant, simultaneous inhales and exhales(see Respiration) and the Speed Force saw no point in figuring out how to add it back since they can eat almost anything organic safely and are immune to 99% of toxins.

Their sense of taste is also a lot less sensitive than a human’s. They basically just taste the rough composition- most things with similar nutritional contents taste identical, and they can’t taste seasonings or spices. They have a lot more types of taste receptors since they don’t have a sense of smell but still need to be able to tell what’s in food.

This means that they taste the nutritional content, not anything subjective. Dark chocolate doesn't taste like "somewhat bitter, quite sweet, quite chocolatey", it tastes like "large quantities of sucrose, saturated fat, monounsaturated fat, moderate quantities of complete protein, carbohydrates, low quantities of caffeine, theobromine, calcium, magnesium, phosphorus, potassium, lutein/zeaxanthin, vitamin A".

They don’t really care about the taste of things, only the texture, and even that not so much. Their cooking tends to be absolutely terrible by non-speedster standards, even when they’re following a recipe, since they tend to burn or undercook it out of impatience and completely ignore the existence of seasoning.

The nasal passages and throat have skin flaps that seal while running, swimming or holding their breath. Much like the ear flaps, they only close involuntarily.

Pain

Speedsters have a ridiculous pain tolerance thanks to a higher threshold to feel it at all- otherwise, running would be quite painful since their healing factor is constantly repairing small muscle tears and microfractures.

 As a result, they tend to ignore wounds after they’ve been initially inflicted. The fact that their healing also suppresses further pain after it starts makes this tendency worse.

[ikibli]

Speedster Biology 101: Respiration

Just a little bit of headcanon, because the Speed Force took one look at human biology and was utterly horrified, and then reworked everything for maximum efficiency at high speeds.

Speedsters have three sets of lungs, and none of them work like human ones.

The primary and secondary sets are almost identical to each other and human lungs, and are smaller and designed to alternate so that one set of lungs is contracting while the other is expanding- thus producing the appearance of inaudible and shallow breathing. (As a side effect, it’s possible for speedsters to talk continuously without ever pausing to inhale. They make great use of this.)

Unless, of course, they’re holding their breath, in which case they exhale once, so their secondary lungs collapse(a somewhat uncomfortable sensation) and their primary lungs mostly empty.

Then their tertiary lungs(which are basically just air sacs) feed fresh air continuously into the primary lungs, periodically making short exhales to vent oxygen-poor air from the primary lungs(which sounds like panting). This can last until all four tertiary lungs are empty, which takes about two hours at rest and just under thirteen minutes in combat or while running.

Speedsters instinctively hold their breath when running, swimming, the air is unbreathable or when highly emotional.

Incidentally, they can survive in space or deep underwater as long as they start holding their breath beforehand, since their lungs are designed to withstand high pressures and repeated collapses and reinflation.

They can talk while holding their breath- though only in very short (1-2 syllable) bursts, since they can only speak while exhaling like humans.

When they’re done holding their breath, they inhale sharply to inflate the secondary lungs(also uncomfortable), then refill the tertiary lungs with a series of staggered inhales while resuming normal breathing with the primary and secondary lungs(which looks and sounds like panting or gasping for air as long as their tertiary lungs aren’t full, even if they’re otherwise breathing normally).

They also can’t voluntarily inhale or exhale more than very shallowly- though since their primary and secondary lungs are already replacing almost all of the air inside them with each breathing cycle, they don’t need to. They do breathe faster when running or otherwise excited, though, which reduces tidal volume somewhat.

They can pant, but they generally only do this when they're overheating.

Sighing is achieved by starting to hold their breath, then stopping before the secondary lungs collapse. (It’s less instinctive than growling or hissing, but they still do it when talking to non-speedsters.)

Young speedsters have smaller tertiary lungs, and those younger than five only have two functional tertiary lungs, the lower two being undeveloped and sealed off.