Hmm, I see what's going on... you're an Old Crow, so you might not have heard of this. There's this newfangled idea of "Germ Theory of Disease". Basically, infections are caused by these tiny little specs of dust that are essentially Everywhere. Worse yet, if you have an aggressive type, any little bloody break on your skin can cause a nasty infection. And those pebbles, they weigh about the same as a man, so for a close approximation of the hit, you can imagine jumping off a horse at full gallop, as fast as a fast steed can; and landing on a sturdy brick wall. Now, that, that's going to cause some of that bleeding. And if that silly theory is correct, that just might be enough. Now, I don't know if I can trust that myself; sounds stupid, how would those specs of dust grow into pustules and swelling? But it's a game, a silly little fantasy, and every hit you take just has that chance... it sounds a little sci-fi, but I can live with it, I guess.
Now, if you'll excuse me, the barn seems to be on fire, I'll be needing to go get me a few buckets...