What is hidden in 3D image?

A newly-married couple came home from their honeymoon and moved into the upstairs apartment they'd rented from the groom's parents.
That night, the father of the groom was awakened from his sleep by his wife. "Tony, listen!" she whispered.
He listened. Upstairs, the bed was creaking in rhythm.
The wife said, "Come on, Tony! Let's make love!" So Tony climbed on top of his wife, and pounded the old bone home.
As he was trying to fall back asleep 15 minutes later, the bed upstairs started creaking in rhythm again. "Come on, Tony!" said the wife. "Let's make love again!"
Once again, Tony climbed on top of his wife and screwed her as hard as he could.
As he was trying to fall back asleep 15 minutes later, the bed upstairs started creaking in rhythm again. "Come on, Tony!" said the wife. "Let's do it again!"
So Tony grabbed a broom and pounded on the ceiling as he shouted, "Hey, kids, cut it out! You're killing your old man down here!"