What is hidden in 3D image?

An army Major visiting sick soldiers, goes up to one private and asks "What's your problem, Soldier?"
"Chronic syphilis, Sir."
"What treatment are you getting?"
"Five minutes with the wire brush each day."
"What's your ambition?"
"To get back to the front, Sir."
"Good man," says the Major. He goes to the next bad. "What's your problem, Soldier?"
"Chronic piles, Sir."
"What treatment are you getting?"
"Five minutes with the wire brush each day."
"What's your ambition?"
"To get back to the front, Sir."
"Good man," says the Major. He goes to the next bed. "What's your problem, Soldier?"
"Chronic gum disease, Sir."
"What treatment are you getting?"
"Five minutes with the wire brush each day."
"What's your ambition?"
"To get the wire brush before them two, Sir."