#these two are tagged because they're outliers in my own headcanon :)

[mwolf0epsilon]

The other day I mentioned that I have a very particular headcanon for how the faces of living engines and other large machines and vehicles work. As promised yesterday evening to the people who expressed interest, I will elaborate on it now!

To preface this headcanon discussion, I won't go into how some engines, cars, planes, other vehicles and/or large machines come to life when others don't.

This is still very much a mystery to not only myself (Because what is the criteria here for what gets to be a living machine? What sets some cars, like Sir Topham Hatt's little blue car, apart from others like Caroline?) but an in-universe mystery as well (That said, for anyone interested in building their own mythos, Japanese Mythology does have something that comes kind of close! Albeit not a complete match, the living machines could potentially be classified as a form of precocious Tsukumogami).

Anyway, onto the meat of the discussion!

To put it simply, the face of a living machine is an indicator of their connection to the world itself, as well as an overall display of their 'health'. It is their very soul taking a familiar more personable shape so that they can better communicate with their creators and surroundings.

When a machine or vehicle is created, the chances of it coming to life are very much an unknowable percentage of probability (the world itself writes it off as 'It is what it is'). They're essentially a blank slate that, when first brought into operation, can awaken into existence itself. You only know for sure if they are alive when their face simply flickers into place, like a puzzle piece being slotted into its rightful spot.

Workshops and factories have protocol for the possibility of waking up a living machine. Two people will be testing the functionality of a newly-built engine, car, etc, while a third person serves as a lookout that will be watching for the appearance of a face.

This is a process that needs to be done gently, as waking up a living machine too hastily might cause more trouble than it's worth (shocking something larger than life into the waking world is a surefire way to give them behavioral issues). There is also a chance that doing it improperly will cause the machine itself to remain dormant (their face briefly flickering in and then disappearing, as they retreat inward to protect themselves from further harm).

While most people are aware that the faces of living machines serve a communication purpose (Example: A car can remind their driver to be wary of road laws and lights, an engine can help their crew by serving as an extra set of eyes, and an airplane can notice a problem before their pilots and engineers), not everyone is aware of a much more important facet to their faces.

That being that, if a living machine is damaged or stressed enough, their faces will begin to flicker in and out as a warning that something might be terribly wrong.

Damage-wise, a flickering face may potentially indicate that the living machine has become too weak and will die if it is not repaired soon. It is always a pitiful sight to behold, as the living machine will be aware that they are dying and will most often be begging for help or even crying in fear. A rather heartbreaking thing to witness indeed (not even they know what comes after death, and the fear of the great beyond is not a unique experience for humans alone).

Stress-wise, a flickering face means the living machine may be suffering psychologically and might retreat inwards to protect themselves from stressors (most commonly seen in engines, planes and other vehicles that survived their service in the wars, but it's not just tied to ptsd). A severely overworked and depressed living machine will lose their face to simply disconnect from the world in an attempt to shield itself, but it often has the opposite effect if the people who own it do not know what caused this phenomenon to occur (many faceless living machines that were still alive have mistakenly been scrapped due to people's lack of understanding).

As a rule of thumb, living machines don't consciously hide their faces. It is a part of them that they accept as being static and ever present until the day they die. To try to get rid of one's own face is often regarded as self-depersonalization. A very taboo subject among living machines.

That said, there is one famous engine who seems to have figured out how to do so voluntarily, and he does so as an expression of his more reserved nature. That engine being City of Truro, who often operates without a face but can communicate without it just as well as any other living machine who has a face.

Only those he trusts most have seen Truro's face, and it's honestly a very big deal.

He wears his smokebox door with pride!

Another curious detail is that prototypes don't usually come to life. If they do, often they have a very muffled voice and don't gain a face at all since they aren't made to last (they are simply proof of concept and might even be rather shoddily built) and will fade away unexpectedly.

Gordon is a rather peculiar case, as he is to date one of very few prototype engines who not only came alive and gained a proper face and voice, but has also remained in working service for a staggering 104 years. That said, he doesn't like it when others find out he's a prototype rather than an actual A1 Pacific, because their treatment of him changes abruptly in the face of such a 'odd curiosity' as him...

He wears his 'pedigree' with pride and must keep up appearances after all... Being seen as lesser is unacceptable.