Rats giggle when tickled.

Science recognizes two types of tickling: knismesis and gargalesis. The former is the “light, feather-like” kind, which doesn’t induce laughter, while the latter is more high-pressure and does cause laughter. And while you may think of humans as the only creatures susceptible to gargalesis, one of our much smaller counterparts is as well: the humble rat. Rats actually love being tickled, especially on their back and belly, and there’s even a specific term for the frolicking they do in between tickles: freudensprünge, or “joy jumps.” Sadly, rat giggles are too high for us to hear without special microphones that can reproduce the sound in a lower register. (That doesn’t make videos of rats being tickled any less adorable, however.)

All of the great apes (gorillas, chimpanzees, bonobos, and orangutans) let out a “remarkably human-like laugh” when tickled, while animals ranging from dogs to penguins appear to enjoy it as well. That said, many humans do not — some find the sensation deeply uncomfortable, and laugh out of discomfort rather than joy. One study in which participants rated how much they like being tickled on a 10-point scale (from very unpleasant to very pleasant) produced an average of only 5. Perhaps surprisingly, people rated tickling others at only 5.9.

In other words, it ain’t funny.