To do this experiment you must be a post-pubescent male, able to growl so that you hear a rumbling sound inside your head. Go ahead: growl at digital displays on VCRs and microwave ovens, neon lights on household appliances, your computer screen, and (sometimes) fluorescent lights.
What happens? Your computer screen wiggles around, since it's actually refreshing the images at a fast rate. The digital display on an alarm clock may actually appear to split in half, some lit segments moving independently of others. In these displays, some segments are lit for an instant, then the others are, then back to the first, and so on. On other devices, any small light or LED will jiggle up and down if it is powered by the alternating current from the mains.
Hold on! You're not actually making these lights move; it's just that your skull and eyeballs are vibrating at almost the same rate as the lights are flashing. Almost the same rate but not quite synchronized means that the light will be bright each time your eye is higher, then a moment later, bright each time your eye is low. If you would not call yourself a post-pubescent male, you can perhaps still vibrate your head by touching it to a machine with a running motor inside: a vacuum cleaner or the body of an electric razor.
Remember to follow instructions and use extreme caution.
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