What is hidden in 3D image?

An elderly married couple scheduled their annual medical examination the same day so they could travel together. After the husband's examination, the doctor then said to him, "You appear to be in good health. Do you have any medical concerns that you would like discuss with me?"

"In fact, I do," said the man. "After I have sex with my wife for the first time, I am usually hot and sweaty. And then, after I have sex with my wife the second time, I am usually cold and chilly."

"This is very interesting," replied the doctor. "Let me do some research and get back to you."

After examining the elderly wife, the doctor said to her, "Everything appears to be fine. Do you have any medical concerns that you would like to discuss with me?"

The lady replied that she had no questions nor concerns. The doctor then asked, "Your husband had an unusual concern. He claims that he is usually hot and sweaty after having sex the first time with you and then cold and chilly after the second time. Do you know why?"

"Oh that old buzzard!" she replied.

"That's because the first time is usually in July and the second time is usually in December!"