"I don't," Childermass confirms. He really doesn't want your fish, Lambert, but if you're going to insist on being terrible at cooking, there's no real choice here. He takes the fish, staking them out on his side of the fire, then settling back down to watch and wait. Unlike the witcher, he's going to be patient, but just in case Lambert continues to wave his hands and set things on fire—

"You have to turn them to the other side when the first starts looking dark enough, not throw magic at them."

Even if Lambert is still so intent on picking out what little there is from the fish he basically ruined, it hardly impresses the magician. He's already sure that it tastes terrible.