I think that foot (the one going forward) carries at least 1/4 of your body weight at the time. So that x how fast you're going = muffled cursing when you stub it.
Your whole foot is stuffed with nerve endings, and the toes have the nerve endings to the brain. That could have something to do with it.
I stubbed my toe before and broke it
Yeah, that happened to me yesterday. Sad day.