I understand the biological processes okay, but I can't figure out where the expressions "go apeshit" and "batshit insane" come from. The first seems like it might have something to do with flinging poo, but the second makes no sense at all.Does exposure to guano cause insanity? Is it just a really crazy situation when a bat shits on you?Dictionary.com is no help, and I don't have access to the O.E.D. Wiktionary mentions the phrases, but it doesn't try to figure out their origins.