what's inside mighty bean toys?

Answer 1

The physics of Mighty Beanz
The toys are hollow and contain small, dense, magnetic spheroids, which are not quite as long in diameter as the inside of the beans, in order to allow for movement. A Mighty Bean can stand up on either end because the spheroid is pulled over the centre by gravity. This pulls the centre of mass of the Mighty Bean over its tiny base, making it impossible for the Mighty Bean to fall down.

When a Mighty Bean is placed on a slant, instead of simply sliding down, the Mighty Bean falls on its side, and the spheroid rolls down and up the other end. In doing this, the ball rolls slightly up the other side of the Mighty Bean, causing the centre of mass to shift away from the Mighty Bean's long base, making it fall over. It stands vertically for a moment, and repeats the process.

Answer 2

I think that there are weights inside and when it tilts, the weight drops to the bottom and moves it.