That's very interesting information...I had a theory that there were sounds that we couldn't hear that call for the frogs to respond. Also, what you said above about playing back your frog's own calls...that might explain why my little guy won't respond to any other frog's croak. I think I've played youtube videos of White's croaking about a dozen times with only one response. And right after he's done croaking, he won't do it again for some time. Very weird.