What is hidden in 3D image?

A crusty old Marine Corps Colonel found himself at a gala event at a posh hotel, sponsored by a local liberal arts college. There was no shortage of extremely attractive, idealistic young women in attendance. One of them approached the colonel.
"Excuse me sir, but you seem to be a very serious man. Are you this way all the time? Or is there something that's bothering you?"
"No, I'm just serious by nature."
Looking over the colonel's ribbons, the young lady said, "You seem to have seen a lot of action."
"Yes, a lot of action," said the colonel rather curtly.
Finding it hard work trying to start a conversation with the colonel, the young woman said, "You know, you should lighten up a little... relax and enjoy yourself."
This didn't seem to move the colonel, who just looked at her very seriously.
Exasperated, the woman said, "You know, I hope you don't take this the wrong way, but when was the last time you had sex?"
"1955."
"Well no wonder you're the way you are! You really need to chill out a little and quit taking everything so seriously. I mean, no sex since 1955 is a little extreme!"
"I don't think so, it's only, 2130 now."