Floors tend to be slippery when wet.

It turns out if you run full speed across a freshly mopped floor, it is entirely likely that you will go careening into the wall. I thought I had broken my leg it hurt so bad, but then I realized that I was standing on it. I'm not sure how well the photos portray the huge swollen knot just below my knee-cap. It is at least the size of a softball, and I'm sure it's going to soon display an alarming resemblance to a rainbow.

Photographic evidence: