This demo of the Mellotron simply has to be seen:

The Mellotron, of course, is a much used cult instrument that works by running a series of short tapes against tape heads when someone presses the keys. I know “much used” and “cult” doesn’t really go together, but in the case of the Mellotron I feel it describes it pretty accurately. It’s been used for over four decades on an incredible amount of records and yet has that eerie warbly tape sound that is simply weird.

The short glimpses of the insides of this incredible instrument are fascinating too. If anyone has better videos of the inner workings of one, please post a link!