Yes, they make a sound somewhere between a square wave and a Kazoo, it's the everso lovely Clavioline at number 8 on our countdown of the Top 20 Weirdest Instruments of all time.
By the way, if you've missed out on any of the other episodes of this series you can catch them all right here where you can check out such oddities as the Fire Organ, the Cracklebox, the Waterphone, the Optigan and lots of mad, strange looking synths.
Things are really hotting up next episode with the most recent instrument to feature on the entire chart at number 7...
I'd give you a clue, but it may have an adverse REACtion. Geddit?