A scene from 'Ghost'
If the ghostly form of the recently deceased Sam Wheat can pass through walls, why doesn’t he sink into the ground?
BEST EXPLANATION: Of course, this question can be applied to most staged representations of non-corporal entities (from the ghost of Hamlet’s father to the spirits that roam the halls of Hogwarts). And there’s no satisfactory answer: it’s just, you know, the way things are.
[youtube=http://www.youtube.com/watch?v=cjkkKO5Gsno]