In 'The Frog King', what object does the princess drop into the well?

In “The Frog King,” the princess drops a golden ball into the well.

The story opens with the king’s youngest daughter playing beside a deep well in a forest. Her favorite toy is a golden ball, which she throws into the air and catches. One day it misses her hand, rolls across the ground, and falls into the water. Because the well is too deep for her to retrieve it, she begins to cry.

A frog offers to recover the ball in exchange for becoming her companion at meals and in the royal household. The princess agrees, expecting the frog to be no more than a temporary nuisance, but she later tries to avoid the promise. In the Grimm version, the tale is not originally centered on a kiss; the enchanted prince is restored after the princess angrily throws him against a wall.

The story is also known as “The Frog Prince,” but its original German title is “The Frog King, or Iron Heinrich.”