Once upon a time there were a dog and a robot. The dog said to the robot: "How about we play a game!"
"Okay!" said the robot. "What game shall it be?"
"Let's do this", said the dog. "I'll hide an item. Then I'll write a clue for where that item is, and then hide the clue. Then I'll write a clue for where that clue is, and hide that. And so on. Then I'll give you the first clue."
"Okay!" said the robot.
The dog went off to write the clues and hide the items.
When she was done, she came back to the robot.
"Here is your first clue", said the dog. The robot read it.
Big, green, has needles
Hmm... that tree over there is big. And it's green. And it has needles, thought the robot, so she went over to the tree, and, sure enough, there was another piece of paper in it. That was easy.
Small, red, flat, lots of them
Hmm... that pile of leaves over there, thought the robot, and, sure enough, there was yet another piece of paper.
Big, blue, to the west
"Wait!" said the dog. "I moved it when finding a place for clue five! It's actually to the—"
But it was too late. The robot had already walked into the river that was to the west in search of the third clue.
Moral: Never leave dangling pointers.