And the baker said, “Don’t you know about that clock of hers? She had it made when her heart died. It’s like a clockwork heart, see?”
“Really?” said Tiffany. “So if her heart died, and she had a new one made of clockwork, how did she stay alive while the new heart was being made?”
“Oh, that’d be by magic, obviously,” said the baker.
“But a heart pumps blood, and Miss Treason’s clock is outside her body,” Tiffany pointed out. “There’s no… tubes…”
“It pumps the blood by magic,” said the baker, speaking slowly. He gave her an odd look. “How can you be a witch if you don’t know this stuff?”

– Boffo |
Terry Pratchett, Wintersmith