Hn, one time, I put a little glass bowl into the tank and put bloodworms into it, of course none of the frogs could figure out the 'puzzle', and I wound up dumping the worms out, but I didn't remove the bowl straight away.
Well, one of my frogs performed a standard-issue Kamakazi Gasp and bolted up to the top of the tank, and dove straight down... into the glass bowl.
Ever rolled a marble around in a bowl? Seen it roll up to one side, back to the other, and then back again? Its path forms a little 'u'?
My frog did that, four times, before he swam away.
It was grand.