Trouble with snake's eyes

I created a snake and made its pupil a separate layer from it. I made that pupil a symbol. Then I used the Asset Warp Tool to give the snake its flexible body. But the pupil wasn't attached to it. I moved the snake and the pupil stayed where it was.

Next I made its pupil part of the same layer as the snake. I was hoping to move the pupil as a graphic symbol. But once the Asset Warp Tool was applied, I couldn't do anything with the pupil.

How do I keep the pupil attached to the snake while still giving it free ability to move?