Now although this is silly and quite crude (You have been warned), it is a legitimate physics question. I was sitting on the toilet a few days ago and I got some splash back. I started thinking about elastic collisions and how no matter what, nothing is perfectly elastic (correct?). Why would the water come all the way back up to my... you know what and not just my cheeks. If water doesn't observe the behavior of an elastic collision, it must be a mass issue. Maybe the mass of water that gets splashed back up is less than the amount of the impacting mass?