Yesterday morning, my mom was quite surprised when she walked into her craft room to discover what we think is a gray tree frog on the floor. It's winter here in Michigan, so it probably came in on a potted plant on her porch she brought into that room in the fall. It probably figured on hibernating in the pot but it's kind of warm in that room so we don't know how long it's been out of hibernation. She put him in a cardboard box and planned to ask a teacher at the school she works at that knows a lot about different animals but that teacher was out ill yesterday. I've been doing some research and suggested we set up a little habitat.

This morning my mom found something that she thought would work for an enclosure, but when she got the frog it appears dead (she was worried about it during out which seems to have happened). We have him sitting on moistened paper towel on the off chance that rehydrating can bring the little guy around, but she said he seems pretty stiff which in most species means rigor mortis and death occurred some time ago. But she has seen fish that escaped the tank and dried out and appeared dead revive when placed back in water amazingly enough. Basically we're not sure how to tell definitively that he has passed. We're pretty sure it's too warm in the house for him to have gone back into hibernation.

Is him being stiff the "dead giveaway" it would be in most animals? If not, at what point do we know he is well and truly dead?

If there is a chance, is putting him on the moist paper towel the right thing to do? Anything else we can/should be doing?

Thanks in advance.