Thanks for your responses. You're right, I didn't give them enough credit for being that smart--it had crossed my mind several times--as I said he is the one who is always investigating. But sometimes he sits and looks right at me. The thing that really shocked me was how he came flying out--my tank is 18" high & I know he wasn't scaling the side--he's done that before, but I would have noticed. There is one plant that goes about halfway up, and he sometimes climbs around in it, but it's really flimsy. Well, lesson well learned for me.