I put a card with mean looking gorilla on it because I like to think, in my frog wonderland brain, that my pixies understand not to bang their heads against that part of the glass for any reasons. And I didn't do it to protect my chameleon. He would just puff up and move on up the vine. I did because one of the pixies didn't get the idea that Rango (yes, I know) was never going to be in his stomach, and he kept bouncing his face against the glass.