What is hidden in 3D image?

One day three people were stuck on an island with cannibals.

The cannibals said, "If you do what we say, we won't kill you".

So the 3 people followed the orders which were to go into the forest and pick 10 fruits of your choice.

So the first person came back out of the forest with 10 apples. The cannibals said, "put the apples up your ass without making a facial expression". The person held his composure however then made a facial expression after the second apple, so the cannibals killed him.

The second person came back out of the forest with 10 cherries. The cannibals said, "put the cherries up your ass without making a facial expression". However as much as he tried to restrain himself the person burst into tears laughing on the tenth cherry, so they killed him.

In heaven, the person with apples asked the person with cherries "why did you start laughing?"

The person replied, "I saw the third person come out with pineapples."