after hearing "simply having a wonderful christmas time" by paul mccartney 74 times while working in retail, I came to the conclusion that they shot the wrong beatle
shapeshifting is something that a basilisk will nearly always seek to do in solitude.
an act which temporarily blinds and numbs the creature from the surrounding world - they will be left completely vulnerable to it. defenseless. frozen inside the shell of their old form as organs and cells rearrange.
to shapeshift in front of someone is, therefore, the ultimate show of trust that a basilisk can perform.