What is hidden in 3D image?

A young man was visiting his brother and sister-in-law for the holidays. As he arrived at their house he found his young nephew, Timmy, helping them bake some cupcakes.

After they were done, his sister-in-law allowed Timmy to put the icing on. When the boy had finished, he brought them to the table.

"The cupcakes look delicious, Tim." his uncle said. He took a bite and said, "Timmy these are so good."

As he finished cupcake and took another, he again complimented his little nephew. "The cupcakes look beautiful, Tim," his uncle said. "How did you get the icing so neat?"

His nephew replied, "It was easy. I just licked them."

The uncle turned pale. He pointed to the plate of cupcakes. "You licked all of these?"

Timmie replied, "Well no. After a while my tongue got tired, and I got the dog to help."