How did acolytes in the 16th century make an egg 'dance' on the fountain of the Barcelona Cathedral's cloister?

A. By emptying the egg and using wax to add weight, allowing it to turn on a water jet
B. By using a hidden string to manipulate the egg
C. By using a magnet to levitate the egg above the fountain
D. By placing the egg on a mechanical device that rotated it
Answer: 