“After a while the Senior Wrangler said, "Do you know, I read the other day that every atom in your body is changed every seven years? New ones keep getting attached and old ones keep on dropping off. It goes on all the time. Marvelous, really."

The Senior Wrangler could do to a conversation what it takes quite thick treacle to do to the pedals of a precision watch.

"Yes? What happens to the old ones?" said Ridcully, interested despite himself.

"Dunno. They just float around in the air, I suppose, until they get attached to someone else."

The Archchancellor looked affronted.

"What, even wizards?"

"Oh, yes. Everyone. It's part of the miracle of existence."

"Is it? Sounds like bad hygiene to me," said the Archchancellor. "I suppose there's no way of stopping it?"

"I shouldn't think so," said the Senior Wrangler, doubtfully. "I don't think you're supposed to stop miracles of existence."

"But that means everythin' is made up of everythin' else," said Ridcully.

"Yes. Isn't it amazing?”