Interesting observation: I feed the frogs Mon-Wed-Fri, thawed-out frozen bloodworms, brineshrimp and glassworms, using metal hemostats in their glass bowl. Inevitably I clink it a bit against the side. Afterwards, I give the rest of the cube to the angelfish. I discovered the other day when I accidentally hit the frog bowl with the metal letter opener, that not only did the frogs get all excited at the sound, the angelfish went nuts, too.
