text: Oooo, that's a good one, and thanks, because I was going to ask a similar question.\nDid you ever look at a fan as you were walking towards it? If you take a heavy step, or stomp, the fan blades will appear to stutter, or freeze for just a second. Sort of a strobe effect.\nI think that this is related to the "bounce" in the computer monitor, which is also presenting moving images (at 60 or 120 cycles).\nMy theory = which has not been confirmed - is that we are seeing a mental/psychological response to momentary interruption of the visual "signal" transmitted to the brain. The brain sort of smooths over the gap in signal, which results in a freeze-frame, in the case of the fan, or a bounce, in the case of the monitor.\nI think the cause of this might be that vision is a chemical process in the rods and cones of the retina. A thump, produced by chewing or stepping, might cause a momentary change in the chemical reaction. \nAnyway, I like your question ... it shows genuine curiousity about why things are the way they are ... which is the basis of good science.