My wife, Jill used to work at the San Diego Zoo and Wild Animal Park for the research unit called CRES (The Center for Research on Endangered Species) in the late 1980s. She did primary behavior research on mother-infant dyads, both as an intern and later as an employee.
In particular, she was involved in behavioral studies involving Lion-tailed macaques, which are an endangered species of monkey from India. The purpose of the research was to find ways to increase the emotional well being of the animals, as some of these monkeys have significant issues breeding in captivity.
There was one mother named Polly and her infant daughter Dewa which were particularly interesting. Polly would let her infant girl nurse for a while and when she was tired of it, she would pull her off her nipple and literally hold Dewa’s head to the concrete floor for about 30 seconds.
Dewa would scream and chitter - with her little arms and legs flaying around. Then Polly would suddenly let her go...