What is hidden in 3D image?

It was at the end of the school year, and a kindergarten teacher was receiving gifts from her pupils.
The florist's son handed her a gift. She shook it, held it overhead, and said, "I bet I know what it is. Some flowers."
"That's right" the boy said, "but how did you know?"
"Oh, just a wild guess,"" she said.
The next pupil was the candy shop owner's daughter. The teacher held her gift overhead, shook it, and said, "I bet I can guess what it is. A box of sweets."
"That's right, but how did you know?" asked the girl. "Oh, just a wild guess," said the teacher.
The next gift was from the son of the liquor store owner. The teacher held the package overhead, but it was leaking. She touched a drop of the leakage with her finger and touched it to her tongue.
"Is it wine?" she asked. "No," the boy replied, with some excitement.
The teacher repeated the process, taking a larger drop of the leakage to her tongue. "Is it champagne?" she asked. "No," the boy replied, with more excitement. The teacher took one more taste before declaring, "I give up, what is it?"
With great glee, the boy replied, "It's a puppy!"