Breaking a Cow on the Chocolate Bar

The 2nd night of Chanukah was Shabbos. Zeidy took out a chocolate bar from a cabinet and started distributing pieces of chocolate to his grandchildren - one square to each child.

When he gave out his last piece he realized that he was lacking one piece, because Yudi, his youngest grandson was still without a piece of chocolate.

Yudi’s brother Yoni understood the predicament and said, “Don’t worry, Zeidy. I’ll split my piece in half and give one half to Yudi!”

His sister Miriam wondered, “But the piece of chocolate has a picture of a cow on it! By breaking that piece of chocolate, you’ll be breaking the cow. Wouldn’t that be the melacha of mochek?”

Question: May Yoni break the piece of chocolate in half?