El león, la cabra y la lechuga.
The lion, goat and cabbage problem is a river crossing puzzle. 
River-crossing puzzles are older than a thousand years and were devised to help children develop logic and reasoning skills.
The man wants to take the animals and the cabbage to the other side. He has a boat that he can use for this purpose, but there is a problem. The man can carry with him only one of the three at a time on the boat.
- If he leaves the lion alone with the sheep at one side, the lion will eat the sheep.
- Similarly, the sheep will eat the cabbage if they are left alone.