This is a good idea - I did do a peek under each hide, and didn't see it, and the substrate isn't thick enough for burrowing. It's a 10 gallon, few places to hide. That said, I didn't pick her up or look too hard under the hot hide because I didn't want to stress her out, so there's that small chance it might be under her or scuffled in with the aspen. I will definitely keep an eye out, I don't need a mouse going bad in there!