To the chimpanzees, grooming not only has an hygenic aspect, it is also important to form and maintain alliances.
They use their hands, fingers, mouths and teeth during grooming, to find small objects in the hairs of the body. Chimpanzees have a very good eyesight and sensitive fingers which allow them to part hairs and pick small objects like ticks or other parasites from the body surface.
Grooming is more frequently observed among adult males and often goes on for a long time. Male chimpanzees at Mahale tend to groom each other reciprocally. Also, they often focus on the face, possibly trying to find signs of loyalty or infidelity in the face of the grommee.
Teddy and Darwin have been observed to form a strong alliance lately. Primus, the current Alpha Male for sure will be concerned. Teddy still is very popular within the group and it seems like he patiently is planing is move to become the next Alpha Male. If he will be able to convince Darwin, who is a very strong male himself and has been amongst the higher rank males for a long time, Teddy has found himself a strong ally in the power struggle against Primus.
Source: Mahale Chimpanzees 50 Years of Research, based on the work of the Japanese Researchers in Mahale and published in 2015.