Mythologically, this could be an insult in a way. The owl represented Athena/Minerva, the god of wisdom, that is why it represents Duo (because duo is smarter obviously). Poseidon was the god of the sea, earthquakes and horses. Calling a horse a donkey is an "insult" I guess. The two didn't get along very well. Maybe Duolingo is insulting Poseidon :O
"Ase": From Latin asinus.
English "ass": From Middle English as, ass, asse, from Old English assa, back-formed from assen (“she-ass”), from Celtic (compare Old Irish asan, Old Cornish asen), from Latin asinus.
Esperanto "azeno": Doesn't give etymology on Wiktionary, but seeing as asinus has several descendents (ES asno, FR âne, Catalan ase, English "ass" among others) I'd imagine it's got something to do with "ase"
Yes! I looked "ase" on the Catalan etymology dictionary and, yes, it comes from the latin form "asinus". In Italian it's "asino" so I'd say that'd be the closest you could get to the latin form. I didn't that in English you could also say "ass", I'd never have thought of it. Thanks!