Well, not really a carcass. Just some bones that were near the outlet of some plastic drainage hose extensions attached to our downspouts. The hose is about 6" in diameter. I puzzled for a while on why there were bones there.
Sometime in the fall, I think it was, the 'possum had apparently tried to crawl into the downspout hose, got stuck, and died. After a good rain, most of the bones were washed out, but the skull and jaw were still inside. I wondered why our dog seemed to be so interested in running out to that spot whenever she was in the backyard.... <eewwww>
Indeed, opossums are not terribly bright. I'm glad that's been the extent of my dealing with them so far.
Cheers,
Scott.