stand over it, and when it launches, let it hit you in the face, the size of the bruise is directly proportional to the amount of force of liftoff, don't forget the blackeye and bloody nose constants. shown by this function here: F=ENB^3 where F is force, E is the eye constant, N is the nose constant and B is the area of the bruised part of the face. remember, this function only applies when it is referring to the face, if it hits you in the chest, you have to use a different formula to calculate F.