electronics.howstuffworks.com

gMgkA TIL a theremin is a musical instrument that depends on electromagnetic fields created around its antennae, which players move their hands or fingers around to change pitch or volume.
OoDBR TIL that NeoPets is effectively owned by The Church of Scientology.
E5gw TIL that sound cancelling headphones work by making a sound exactly 180 degrees out of phase with any unwanted noise. The sound-wave that it sends out interferes with that of the original sound. The two sound-waves cancel each other out and create silence.