Hmmm, not a bad idea KH
In an effort to save water, one of the guys I was with did suggest they all scrub their armpits on the way down to save having a shower later
I can only assume they make the water soapy to make it more slippery for the people inside the ball (and hence more fun!). You sure can't stand up inside for more than a second or two once you're on your way down that hill!
The closest I came to an injury was when I go kneed in the mouth by my brother whilst trying to pull me into the ball - you have to kinda dive in through a little tube to get into it. Coming out of the ball at the end is probably the most fun thing for the people watching, it's a very undignified process. You have to slide out feet first and plop onto the ground in the midst of a load of water - Taffy said it looked like a cow giving birth
