For some reason, these chimps have begun sticking single long strands of grass into their rear ends — and then just, uh, letting that grass hang out.

This sort of thing — using grass as part of chimp fashion, that is — isn’t new. Fifteen years ago, a chimp at the sanctuary began putting grass behind her ear, apparently encouraging others to do the same.

Now, they’re doing it again, but this time, they’re sticking the grass *into* their ears — and also their behinds. Experts think they may have learned the ear thing from their human caretakers, but as far as the booty thing is concerned, yeah, we have no idea.

Anyone have thoughts?