h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Once upon a time (60s to 70s) my parents had the ultimate non electric can opener. It was a bolt to the wall model that actually worked. The magnet was so strong it not only held the lid, but supported the weight of the whole can. You simply put the can on the magnet, wound the handle backwards half a turn to lock the can in place, then wound the handle a few times and the lid was safely and cleanly removed. The bloody thing never failed and lasted for about twenty years. This efficiency no doubt explains why you can't buy a "Can-O-Mat" any more.