A form of
muscular contraction that propogates itself down a body or organ. In humans, it pushes food through the
digestive tract by propagating a kind of
wave of contraction down the tube.
Snakes can also use peristalsis as one of their modes of
locomotion.
You can buy a peristaltic pump that uses the principle of peristalsis to move viscous material through a flexible tube.
I find peristalsis interesting, in that can be a highly recursive process; each muscle involved can trigger by reflex the actions of the next one. Want a demonstration? Try swallowing. Then try it again, but try to only use the first two muscles you used before, then stop.