Actually, we have had a few instances like this happen to us.

Not specifically deer, but raccoons, dogs, etc who were alive at the time of getting pulled in by the gathering chains on the head.

The worse part is, often, the reverser, which sends the chains and feederhousein the opposite direction, gets stuck. Guess what happens then? You get out and pull the dead or half dead animal out of the gathering chains.

I am going to assume that this deer was either wounded or dead when he got stuck in the head. But then again, there's a reason why we sometimes get that, "deer in the headlights" look.