Aside from anecdotes, we know very little about nonhuman primate laughter and humor, but some of the most significant findings to emerge in comparative science over the past decade have involved the unexpected discovery that rats —
particularly juvenile rats — laugh.
Rats are
particularly ticklish, it seems, in their nape area, which is also where
juveniles target their own play activities such as pinning behavior [when one
rat pins another on its back].