Y'all are pretty darn clever, the answer was teeth. However I'm not sure why y'all were guessing all these other critters... sheep, goats, cows, a carnivore, squirrel, opossum... Seriously? C'mon you know me, they're horse teeth!!
Really and truly they are. The chew tin had mostly wolf teeth and bridle teeth. Some were cut off and some had the roots, which would probably be why some appeared canine like.
The stories this guy has, wow! He's been involved in horses pretty much all his life (he's in his late 60's) He's shown horses, been a farrier, bred & raised horses (actually he still does some of that)
Every time Dale is out I learn something new from him. Sometimes its something practical, like a colt handling tip he demonstrated with Tavi. Sometimes its something that comes out in a story, like horses can get addicted to pain killers (that was a pretty funny story actually)
Dale collects teeth and he pulled some of his collection out to show us. There were those teeth in the tin and a bunch of others as well. Some of them had a story, some didn't. The one below came from a Welsh pony stallion:
Teeth can cause all kinds of issues. They can manifest in how your horse behaves under saddle, his ground manners, how he keeps weight on (or rather doesn't keep weight on) Some horses are pretty stoic though and don't give you a lot of clues. Also your horse can't tell you when he has a tooth ache so its a good idea to get them at least checked regularly.