[…] we have been documenting the spread of a new tradition in Pelon group – eyeball-poking. In this ritual, one participant inserts its finger in the other’s eyeball, slipping the finger deep between the eyelid and the bottom of the eyeball up to the first knuckle. As in handsniffing, the pair remains in this posture for up to several minutes, and often the one being poked in the eye inserts fingers in the partner’s nostrils or mouth during the eyeball-poking.
Capuchin monkeys have it figured out:
https://www.sscnet.ucla.edu/anthro/faculty/sperry/ctp.html