Animal testing on non-human primates between the monkeys natural behaviors versus the behaviors expressed by the diazepam induced monkeys in thirteen different locations inside the maze. Scientist Barros and his colleagues created this model to allow the monkeys to roam a less confined environment and slightly eliminate outside factors that may induce stress. Many of the best-known allegations of abuse made by animal protection or animal rights groups against animal-testing facilities involve NHPs. The so-called "pit of despair" was used in experiments conducted on rhesus macaque monkeys during the 1970s by American comparative psychologist Harry Harlow at the University of Wisconsin–Madison.<ref name="Blum1994/95">Blum, Deborah. "The Monkey
Rhesus macaque between the central and peripheral males. A subgroup of subordinate, often subadult, males occupy the very edge of the groups, and have the responsibility of communicating with other macaque groups and making alarm calls. Rhesus social behaviour has been described as despotic, in that high-ranking individuals show little tolerance and frequent and often severe aggression towards non-kin. Rhesus macaques interact using a variety of facial expressions, vocalizations, body postures, and gestures. Perhaps the most common facial expression the macaque makes is the "silent bared teeth" face. This is made between individuals of different social ranks, with the lower-ranking one giving