Movie composer Mark Korven   wanted to craft the perfect sounds for horror movies, but the instruments he needed didn’t exist, and he was tired of using the same digital samples. To produce the original effects needed for evoking breathtaking moments of suspension, he teamed up with guitar maker Tony Duggan-Smith to craft an original instrument that would better aid in manufacturing fear. The Apprehension Engine is that tool, a mechanism built with several bowed metal rulers, spring reverbs, a few long metal rods, and other attachments that allow for spooky interludes and effects.

Source: The Apprehension Engine: An Instrument Designed to Play the Music of Nightmares