Okay, having listened to a whole bunch of calls from various creatures on-line, I think the Thing That Went “HNAAAGH” was a frog. I’m not sure what KIND of frog–the American Bullfrog was pretty close, and I am ashamed to admit that all this time, I thought bullfrogs made that classic “erRRRiBBit!” noise, but it is indeed a sort of flat buzzing “hnAAaaGH!” I’m not sure if that’s the right kind of frog–why the supposedly nocturnal frog was awake in the hottest part of the day, calling moodily across the swamp is a mystery–but having exhausted my brain with frog calls and egret calls and cormorant calls and heron calls (and a more ungainly array of squawks you’ve never heard–those birds sound like Tom Waits suffering severe gastrointestinal distress) I’m willing to chalk it up to “Probably a bullfrog.”

So, um…what the hell kinda frog goes “Ribbit” then?