Today a pupil who had been revising came up to me and said "Do you know anything about biology?"
"Of course, I know loads about everything"
"Can you help me with this picture" he said and showed me this
(PS I have numbered the parts I refer to)
heart

"AH yes I know this well" I said. "This is a map of Birmingham. The blue bit (1), that's the Birmingham ship Canal. The bottom bit on the red (2) that's where the Chavs live. A bit further up (3) that's where the posh people live, trying to keep away from the Chavs. And the pokey out bits at the top (4) .. well that's Spaghetti Junction!

Yes. This is definitely Birmingham!"

He looked at me.
There was a pause
"Oh" He said. "I though it was the heart!"