What is "jittered"

Usage examples of "jittered".

There was a popping sound and he jittered back and forth behind the wheel like a badly managed puppet, his fist digging the pen in deeper and deeper, up to the halfway mark, then to the three-quarter mark, his split eyeball now running down the side of his face like a freakish tear.

One leg jittered impatiently, and her teeth skirled slowly across each other.