Due to the overwhelming demand, I feel forced to tell it.
"Once upon a time there was an adventurous female brain cell. One night, she slipped quietly away from the others, and burrowed out through her owners ear. She clambered across the pillow and came to another ear, and pushed through the thick ginger undergrowth to get inside the head.
When she arrived, it was not at all what she was used to. Instead of the constant babble of girlish chattter, it was very quiet. She began to feel frightened. "Hello" she called, "Is anyone there?" For a moment it was silent.
Then, from far, far away, she heard an echoing voice in reply.
"We're down here" it said.