What is a wallaby thinking?

The stillness is the first half of a decision. A wallaby's default is to hold, work out what you are, and keep the option of leaving open - the ears swivel independently while the body stays locked, which is why they read as unbothered when they are anything but. The moment the maths comes out badly, they're gone, and they do not look back to check.

The leaving is absurdly cheap for them. A macropod's hindlimb tendons store and return elastic energy like a spring, so hopping gets more efficient as it gets faster, up to a point - the opposite of running. A wallaby holding still in front of you is an animal that knows exactly how little the exit will cost.