A vampire bat came flapping in from the night, face all covered in fresh blood, and parked himself on the roof of the cave to get some sleep. Pretty soon the other bats smelt the blood and began hassling him about where he got it. He told them to nick off and let him get some sleep, but they persisted until he finally gave in.
"OK, follow me", he said, and flew out of the cave with hundreds of bats behind him. Down through a valley, across a river and into a huge forest of trees.
Finally he slowed down and all the other bats milled around him, tongues hanging out for blood.
"Do you see that large oak tree over there?" he asked.
"YES, YES, YES!!!!" the bats all screamed in a frenzy.
"Good!", said the vampire bat, "because I didn't".