What's all the racket?

The people above us keep making hugely loud *BANG* sounds, to which we have begun responding with protesting taps of Julie's tennis racket on our ceiling. However, these people are rather tiny, and we have not been able to discern how they can physically accomplish such noise. Today, we journeyed once again up the stairs to discuss the problem. We have now concluded that a possible cause of the stomping sounds is that someone is being naughty & keeps falling off the bed.