Theres a little lip where the screen mesh top sits on the plastic on top of the aquarium.
The gap between the plastic and the mesh screen top is about an inch, maybe less.
He was sticking his head in it and pushing as hard as he could to try to get the lid off.
Ill watch him and make sure he doesnt do it again, I have a feeling it was a one time thing because he has only been with me for 3 days now. Im guessing that he was just curious
So we'll see what happens
Thanks!