The science of shaking Christmas presents

Researchers at the University of Michigan have been studying people shaking boxes in order to shed light on "epistemic action understanding." Or rather, "Can one person tell, just by observing another person’s movements, what they are trying to learn?"

In other words, as you watch someone shake a box, can you figure out what information they're trying to gather about the contents of the box (i.e. the shape or quantity of things in it)?

More info: "Seeing and understanding epistemic actions"