They said they've seen a woodchuck come down a tree head first? Idk if I'm buying that. I think they saw a possum. Pretty much any animal that climbs is going to be able to come down head first. Raccoons obviously but they aren't doing any zigging and zagging and the tree has to be pretty rough. Squirrles are just no fucks given, literally balls to the wall. You even seen one of those little guys run headfirst down a brick wall at full speed? There's not another mammal in North America that can do that. Can't be many in the world.