Stereotypy

Also known as "Animated GIF Syndrome," stereotypy affects captive animals and people with mental illness. Stereotypies are repetitive, ritualistic movements that include nail-biting, vocal tics, "polar bears rocking in place or swimming in endless circuits, parrots grooming themselves until they bleed, gorillas regurgitating and re-ingesting meals, and big cats pacing the same routes in trance-like patterns." I hate watching it. And it's just as bad to dream you're doing it.

It's probably so hard to watch for the same reason it's disturbing to see people's internal organs. Living things usually seem complete, and when organs or behaviors are set apart you can't help but realize that whole depends on inhuman parts. When you watch a cat pacing in its enclosure, never leaving the path its footprints have dug into the floor, you stop seeing an animal and start to notice fur and weight and legs. Watching a living thing glitch is almost like watching it die.

It's less obvious when it happens on larger scales. Lifelong stereotypies aren't so out of the ordinary and don't usually remind us of death.

Evidence for a Relationship...
"Evidence for a Relationship Between Cage Stereotypies and Behavioural Disinhibition in Laboratory Rodents" is a 2002 paper that establishes a neurological link between stereotypy, hyperactivity, autism and the effects of amphetamine treatment. It locates the problem in the striatum of the basal ganglia system. It also finds that stereotypic animals "may experience novel forms of psychological distress." It's a good start.