The dancing monster is an amazing example of elegant engineering. It actually does everything using a single electric motor and some gears. In the following pictures, we have removed the clothing and outer plastic shell to look at the underlying framework:
When the button on the base is pressed, the song "Monster Mash" begins to play. After a second or two, the motor (Figure 2) begins to spin. It spins in one direction, then changes direction and spins in the other direction in time with the music. The shaft of the motor is connected by a rubber belt to a larger wheel. Using a larger wheel gears the tiny motor down enough to match the timing of the music.
A metal shaft connects the large belt-driven wheel (Figure 3) to another wheel. As the motor spins the belt-driven wheel back and forth, the motion is transferred to this second wheel. It has a plastic knob (Figure 4) that fits into a long slot on the inside of the monster's back and works like a cam. The monster's back and front body panels are connected together and attached to the frame by two metal pins (Figure 5) that allow them to move back and forth on the frame. As the knob moves from side to side within the slot, this movement translates to sideways movement of the entire body.