What is hidden in 3D image?

A man goes to a bar with his dog. He goes up to the bar and asks for a drink. The bartender says "You can't bring that dog in here!" The guy, without missing a beat, says "This is my seeing-eye dog." "Oh man, " the bartender says, "I'm sorry, here, the first one's on me." The man takes his drink and goes to a table near the door.
Another guy walks in the bar with a Chihuahua. The first guys sees him, stops him and says "You can't bring that dog in here unless you tell him it's a seeing-eye dog." The second man graciously thanks the first man and continues to the bar. He asks for a drink. The bartender says "Hey, you can't bring that dog in here!"
The second man replies "This is my seeing-eye dog." The bartender says, "No, I don't think so. They do not have Chiwauas as seeing-eye dogs." The man pauses for a half-second and replies "What?!?! They gave me a Chihuahua?!?"