[paula.m.moore]

All of my boy pigs have done this at some point. One pig actually prefers sleeping up there on top of the hay.
Sometimes when they know I am going to trim their nails or do other grooming, they jump into their hay rack (also a Target grid zip tied to the cage) and think I won't see them sitting in there.

I suppose the potential for injury does exist, but I personally have never worried about it with my guys.