Richard Devine explores the sound design possibilities of the Knas Ekdahl Moisturizer, a spring reverb where the springs are exposed so they can be played/hit/fiddled with:

I was just playing around this afternoon with various objects, magnets, marbles, tuning forks, mechanical bugs, and slinky coils. Running the audio through a Tiptop Z-DSP. Quite fun.

Details on the Ekdahl Moisturizer are available at the Knas site.