From www.chimpanzoo.org
During times of relaxation, a chimpanzee may often be found grooming another chimpanzee or its own hair.
Grooming helps to maintain friendly ties among family and community members and to lessen the stress of infants during weaning.
A chimpanzee may request or solicit grooming by approaching another chimpanzee and getting their attention by presenting a part of its body for grooming.