The animated image above doesn't do the motion justice. Here is a YouTube video that shows the butterfly in action:
Each Electronic Butterfly in a Jar is a jar with a wire in it. The wire has a fake butterfly on the end. Somehow, when you tap the top or make a loud sound, the electronics in the cap make the wire wiggle. This creates the very realistic illusion of the butterfly flittering around your jar. It even just stays on the glass and flexes its wings sometimes.
The butterflies come in pink, blue, orange (Monarch), and yellow.