Back in the days of 35mm film, a 50mm prime was considered a 'standard' lens. That's because it gives pretty much the same perspective as viewing a scene with the human eye, without the magnification of a telephoto lens or the shrinkage a wide-angle lens uses to squeeze more into the frame.
The flexi disc (also known as a phonosheet or Soundsheet, a trademark) is a phonograph record made of a thin, flexible vinyl sheet with a molded-in spiral stylus groove, and is designed to be playable on a normal phonograph turntable.
Jumping Discs - Set of 3. These little metal discs are bimetallic - they are made from two different metals - and this enables them to perform an amazing physics trick! The disc is slightly curved, and if you heat the disc in your hands you can then 'pop' the disk so that it bends the other way.