How do dogs get themselves in such trouble?

This week-end I started noticing blood on the floor in the kitchen - and more blood on the floor by the bathtub. Since my dog pepper is the only one who likes to sleep in the bathroom, I knew it had to be coming from him, but why?

I checked his feet - no cuts. And then I made him stand up, and there right on the part of his backside that hits the floor when he sits, was a glob of bloody hair.

With the help of my clippers, I discovered a cut about an inch long - not deep enough to warrant stiches, thank goodness. I treated it with ointment and applied a bandage, which stayed on for perhaps all of 5 minutes.

But why? How does a dog get a cut on his "sitter-down" parts? We don't keep knives embedded in our floors, there are no barb wire fences that he can't run under without hitting the wires, we don't live in an area filled with sharp rocks - I can see nothing here to put a gash in a dog's hind-end.

I guess I'll never know the answer. I'll just be glad the gash wasn't deep and aside from wincing when he sits down, Pepper is none the worse for wear.