Peristalsis occurs in all parts of the human gastro-intestinal tract between the oesophagus and the anus that are not under voluntary control.
Control of peristalsis is entirely involuntary and is mediated by the enteric nervous system. It works by simultaneously contracting smooth muscle in the area of gut above the bolus of food and relaxing the area just after it. The autonomic nervous system can affect peristalsis, making it slower or faster or even work in reverse (it's called vomiting or emesis).
I seriously wonder about the word peristalsis as used to describe snake movement in bitter engineer's writeup above. Can someone get a definite answer? (I'm not an expert on snake movement)