Searching for the bottom

"It's somewhere on the bottom," the Doctor rubbed his hands nervously.
"Tardis has a bottom?" Jamie seemed confused.
"Everything has a bottom, Jamie. Tardis has many - pool's bottom, the bottom of every control column, countless bottom drawers."
"Ah, I see" Jamie cheered up. "And you forgot on the bottom of what you left it."
"Yes, Jamie."
Sitting down, he sighed and blew a tune on the recorder.
"Oh, I remember," he jumped up and retrieved his favourite top hat.
"Where was it?"
The Doctor pointed.
"On the top shelf?"
"No, Jamie. Turn it upside down and it's the bottom shelf."