It was played with a Theremin, a musical instrument that used the field effect of the human body to play.
My favorite movie, saw it when I was 9 I had nightmares for days. Lol
The invisible ID monster is actually pretty scary. That and the weird electronic music. This is pre-Moog synthesizer stuff done with tube amps. Amazing!
https://www.youtube.com/watch?v=YSFoILcyqAU
It was played with a Theremin, a musical instrument that used the field effect of the human body to play.