They do indeed climb, and live, in trees. However, an adult possum lacks the tail strength to hang from its' tail, as reported by some. The young may accomplish this feat for a few seconds, due to a smaller body mass, but to hang upside down and pretend to be batman, it just ain't gonna happen. They do make a resounding "THUD" when they lose their grip, or just fall asleep, and fall out of a tree, almost always landing on their back. This would put you and me in traction, however a possum doesn't seem to worried about it. At least at the moment of impact. Of course the possibility exists they are playing the macho act, and then later go to the possum ER for a workup.