I've definitely run into this with attic fans where birds got into the attic and got sucked in. What a mess! At one site, the home of an elderly couple, this had happened many times over the years to the extent that there was a mound of rotted carcases below the fan. It wasn't until the fan failed that the homeowner called us for service and I discovered their "collection". My guess is that it was around 50 dead birds. Talk about stink!
I had another case where a snake managed to get into a bath fan exhaust outlet that was about a foot off the ground. The flapper had failed, so he just came right in. He managed to wrap himself into the fan enough to the extent that when it was turned on, it whacked most of his head off. Yes, it was a high-quality Nutone fan with a squirrell cage blade. Imagine my reaction when I pulled the cover off and half a snake fell out. I took the rest of the afternoon off to go home and change my pants.
