What is hidden in 3D image?

Two private detectives were doing some research on a scandalous divorce case in LA. At the husband's request they staked out the wife's bedroom, and sure enough, she had another man inside. The detectives remarked to one another that they were going at it as if sex was going out of style.
After watching rather furtively for quite a few minutes, one detective finally said, "As long as we’re here on the case, may be we should go in after him?"
To this the other replied, "Great idea! Who first?"