What is hidden in 3D image?

Sam consistently caught more fish than anyone else. Whereas the other guys would only catch three or four a day, Sam would come in off the lake with a boat full. Stringer after stringer was always packed with freshly trout. The warden, curious, asked Sam his secret. The successful fisherman invited the game warden to accompany him and observe.
So the next morning the two met at the dock and took off in Sam's boat. When they got to the middle of the lake, they stopped the boat and the warden sat back to see how it was done. Sam's approach was simple. He took out a stick of dynamite, lit it, and threw it in the air. The explosion rocked the lake with such a force that dead fish immediately began to surface. Sam took out a net and started scooping them up. Well, you can imagine the reaction of the game warden. When he recovered from the shock of it all, he began yelling at Sam. "You can't do this! I'll put you in jail, buddy! You will be paying every fine there is in the book!"
Sam, meanwhile, set his net down and took out another stick of dynamite. He lit it and threw it in the lap of the game warden with these words, "Are you going to sit there all day complaining or are you going to fish?"