The rattleback is one of those curious creations that looks so simple it's difficult to imagine it doing anything. Until you start spinning it that is.
A smooth oval piece of hard coloured resin, the rattleback is flat on one side and curved on the other.
Place it on a flat surface, curved side down and give it a good clockwise spin. Watch in amazement as the spin stops, the rattleback wobbles back and forth, then starts spinning in the opposite direction!
Tap the stationary rattleback at one end, to set it rocking back and forth, and watch it start spinning!
How does it do that?
There are all sorts of myths associated with the rattleback: Its counterclockwise spin is said to be caused by divination, magic, the Earth's magnetic field and the Fourth Dimension. Spooky.
The truth is actually that the spin is caused by the specific alignment of the long axis of the ellipsoid in relation to the the long axis of the flat top.
So you can amaze people with your scientific knowledge, or tell them you're doing it by using amazing telepathic powers, the choice is yours.
You'll get two rattlebacks in the pack.