A foot or hand that falls asleep feels very weird. First, it is numb and heavy. Then it is painful and tingly. These strange feelings aren't caused by your body snoozing. They're from the squishing of your nerves. The fancy name for this feeling is neuropraxia.

Nerve cells send messages back and forth between your brain and your body. They're very delicate. Most big nerves are buried within muscles and near bones. This protects them from injury.But if you sit on your foot, you press a nerve between your bone and the hard chair. Blood still flows to your foot. But the pressure affects the signals sent by the nerve. When you get off your foot, you release the nerve - and new signals shoot through it. You feel "pins and needles," just as you do when you wham your funny bone - the nerve in your elbow.

- A compact disc player uses lasers, computer chips, mirrors and lenses to read a disc. The disc's surface looks smooth and shiny. But under this surface are tiny pits.

These pits and the track surface around them are both codes. To read the codes on the disc, the player shoots a laser beam through mirrors and lenses at the bottom of the disc.

If the beam hits a pit, no signal is produced. But if it hits a track surface, the beam gives off an electrical signal. A microchip then changes the signal back into the sounds of music.

The laser reads the disc from the center out to the edge. The spiral track it follows is too narrow to see - even though it's a couple of miles long!