Xel considers this very carefully, and then says, just as carefully, "If there's one of those here, they're so well hidden that they must be much too busy to bother with you. However, I don't propose to teach you to do that. Stick to marbles."
Xel hums cheerfully, soaking in the foood.
"Yes, you would," Xel agrees cheerfully--and just a touch dreamily. "People seem to have a little problem running away from here, you see," he explains. There's no reaction to the declaration of cowardice; Xel's Guild didn't see it as a vice, so as far as he's concerned Rincewind has just declared that he has a big nose: very evident to everyone and not very meaningful. "You wouldn't want a cave, anyway," he points out. "They have backs."