Why does a Lister’s corn hurt when I run

I recently did an episode where I was talking about Lister’s corns. If you missed it, a "Lister's corn" is really just a callus or thick skin that looks like the pinky toenail or the little toenail has a split in it.  That edge of the nail that looks like a completely separate piece of nail. But it's not a nail at all, it's callus.   I just saw a runner who had this problem where his Lister's corn was really painful. It hurt so much he thought the nail might be ingrown. He asked, Why does a lister’s corn hurt when I run?    Well, that's what we're talking about today on the Doc On The Run Podcast.