I had quite a ding-ding with someone about the onion thing. They insisted that sleeping with a cut onion next to the bed meant you would never catch a cold as the onion absorbs viruses out of the air. Apparently you only catch colds at night, from the viruses that are floating around in the dark. How they get into your bedroom (and only your bedroom) is anyone's guess. Perhaps they hitch a ride on a passing fly then lie in wait, ready to pop into an orifice while you're sleeping.
When the onion turns black it means that it's 'full' and you need a new one, apparently.
People that stupid should have their right to vote rescinded.