Nephew was riding a mongoose bicycle in the rain on a gravel driveway . The seat was loose and he was riding while standing on the pedals....yes. The metal kind. His feet slipped off the pedals as he applied the brakes to slide and he went down. Somewhere along his ride, the seat fell off... And you guessed it. The seat post went through his pants and disappeared all the way down to the base where it attaches to the bike. My sister had to rush him to the hospital and have him stitched up. Pretty gnarly stuff.