one christmas when i was a kid, i got a yo-yo that had a flashing light on each side of its disc. it was battery-powered, and when you yo-yo-ed it, the lights flashed on and off. i seem to remember the lights shining through translucent coloured plastic. now, it came to pass (:-)) that yea, the batteries did become flat or misplaced, through some process now unyielding to mine retrospective eye, and yet with an optimism borne of youth, i did continue to spin the yo-yo, and the lights therein didst continue to flash. i started showing adults and asking them what was going on, and my uncle roger said "maybe it's some kind of dynamo".

that rocks. i love that from the age of about 9 or 10 i'd been exposed to the concept of the dynamo, even if it wasn't the actual explanation for what was going on.