We've found all of the usual hardware, but the most memorable items we've found have been alive(well, sort of).
This has happened twice to me. Cutting down a hollow oak tree. Half way through the chain binds up, I pull it out to find bits of hair and bloody stuff wrapped around the chain and sprocket. Really nasty. Turned out to be a possum living in the tree. I now try to remember to check out those cavities before cutting.
We've also found many snakes, squirrels, racoons, rats, owls, and bats. Most manage to escape unscathed. My crew called me the "butcher" for a while. Hey, it was an accident, I didn't know he was in there. Really, we do try our best to relocate any wildlife we run into.
I just remembered, I had a rat jump onto my chest while trimming a palm. I was on the top rung of a 30' ladder and tied in with a lanyard, nowhere to go. Before I knew it, he ran up onto my shoulder and then bailed out to the ground. Anyone else have any close encounters with animals?