A Glow Worm is a plush children's toy from the 80's. They were little worm shaped things with segmented bodies, and when you squeezed or hugged them, their faces would light up. They ran on D cell batteries, and the way they lit up was that as you squeezed them, you squeezed a lever together that completed the battery circuit, powering the light bulb in their face. I had one as a child that was green, and he wore a little green pajama hat. He was one of my most valued childhood possesions, and I still have him somewhere.