My dog Jake has a bubble of some sort between his toes and he doesn't want to use that paw. After he's kicked it quite a bit, it has had some blood discharge from it, but nothing serious. He has had this before but it's never slowed him down so much, and has never bled. Since he's eating and drinking and does hobble over when he hears someone getting a cookie over, I don't think it's an emergency, but I thought I'd ask who else may have seen this before.
It's probably some sort of cyst. I don't remember the name off the top of my head; but someone else here surely will.
Google or Yahoo interdigital cyst.