I think 1, the big toe of the front foot is too long. I tried hard when I ran the stairs. It may have broken. So is my dog. He won't let us see his feet. The main reason is that Tiger Claw didn't cut it. This is longer than the above, he can't grind it out by himself, and it is not easy for others to see it, so it is generally easy to ignore it. Pay attention to cutting your nails from time to time.
Step on something you shouldn't.