We’ve talked about the importance of grooming among chimpanzees before, and it’s pretty well known what an essential aspect of life grooming is for most primates. Below is a video of very good friends Burrito and Foxie grooming, with Missy (off-camera), occasionally also grooming Burrito.
There’s a lot of cool things about grooming. In a comment on a post back in 2009, I mentioned some of the following:
The basics: aside from the social aspects, grooming is the removal of dirt and debris and the tending to wounds (licking and picking scabs). It’s why chimpanzees don’t need baths – they do a really good job of cleaning themselves and each other – no water necessary.
The debris found on the grooming partner is not necessarily consumed, even though the lips are usually involved in grooming because chimpanzees use their prehensile lips, almost like another set of fingers, for many activities like inspecting objects, turning the pages of a magazine (in captivity), and especially in grooming.
Increased grooming often occurs after a conflict to reassure and/or “make up” with one another and to cement social bonds. Grooming has a calming affect, which is easy to see when you observe chimpanzees grooming one another. A study of wild chimpanzees that used non-invasive methods to collect urine samples after grooming bouts found that oxytocin (sometimes referred to as “the love hormone”) levels were higher in bonded grooming partners than in samples collected of chimpanzees who had not been grooming or had been grooming with a “non-bond partner.”
Regarding lip movements during grooming: it is common for chimpanzees, as well as other primates, to “lip smack” or “teeth clack” or make other “sympathetic mouth movements” when grooming (also when performing other fine motor behaviors – like many of us who move our tongue a certain way when we’re really concentrating on a task).
Each chimpanzee does his/her own thing, Burrito is a lip smacker (he may teeth clack on occasion too), Foxie is a teeth clacker, and Annie makes raspberry sounds with her lips. The intensity of the mouth movement/noise will increase if something (especially a wound or scab) is found during grooming.
Some scientists have hypothesized that these sympathetic mouth movements were an evolutionary step towards spoken language. Our friend Gabriel Waters and [former] Central WA University professor Dr. Fouts published a study on this theory a few years back: http://cat.inist.fr/?aModele=afficheN&cpsidt=1349990, and there was a book with this premise called Grooming, Gossip, and the Evolution of Language, which I admittedly still need to read, that argued that gossip for humans is what grooming is for chimpanzees and other non-human primates.
So, with all that information, here’s the video of Burrito and Foxie strengthening their friendship through grooming today: