A British company called Grand Illusions sells “talking tapes” — strips of plastic with patterns of ridges on them that turn into audio when you scrape them over your teeth or attach them to an amplifier (such as a balloon) and run your fingernail on them.
A long thin plastic strip, about 60cm long. It doesn’t look like much, but it talks! Along the length of the strip is a pattern of fine ridges or lines. Run your thumb nail along the ridges, and the tape speaks. However the sound needs to be magnified, so that you can hear it. One method is to hold one end of the strip between your teeth. Then, when you run your nail along the strip you hear it talk, but no-one else does. Or you can stick one end of the strip to an inflated balloon or a paper cup using sticky tape. The balloon or cup acts as an amplifier, and you can then demonstrate it to anyone nearby. Never heard a balloon talk? You have now! What do the tapes say? One says ‘Happy Birthday’ others say ‘Congratulations’ or ‘Have a Nice Day’. We have 5 different messages, and we supply 4 tapes of each message, making a pack of 20 Talking Tapes.
(via Neatorama!)