scratch. Scratch vigorously skin of anothers back or arm at beginning or middle of grooming bout, usually with one hand, making audible sound. Absent at Gombe as tradition but seen in one male and two females in 2001. Bonobos of Wamba occasionally scratch another with first and second fingers in grooming. Category. See video. scratch socially, poke type When scratching another at Mahale, few rarely poke with straight fingers. Customary among chimpanzees of Ngogo. 9. See video. scratch socially, stroke type When scratching another at Mahale, usually stroke gently with bent fingers. See video. scream Goodall:.high pitched and loud, almost always given in a series. Usually heard in contexts of aggression and general social excitement by highly stressed, fearful, frustrated, or excited individual. See also squeal in copulation