Runic magic. [He gets another towel out, this one much smaller, and shows Dumbledore the runic circle stitched in with thin thread.] It releases the heat you've stored in it when you break the runes on here.

[As Dumbledore mentions his world, Merlin seems to tense a little before forcing himself to relax. His smile still lingers, though it's turned a bit wry.]

I wouldn't mind sweets. I suppose that's better than "Merlin's beard" or all those other phrases.