That's what I figured, but it seems like someone could come up with a logical reason to pick something else, like cow is the only herbivore or something. (I don't know if that is true.)My initial reaction was to choose goat...a four-letter word amongst a bunch of three-letter words.
After reading the side note, I reasoned it was the only domesticated animal that that we (ethnocentric we) didn't keep for dietary purposes.