Childermass cannot help the quirk of his mouth that appears at Norrell's fussing. "I have no doubt that they are taking their time to vex you, sir, but they will arrive in time. As you will see. In the meanwhile, will you tell me what pressing engagement you may have, so that I may better apologize for keeping you."

He knows very well that Norrell likely as not has absolutely nothing on his agenda and is just itching to get out of there and back to the safety of hearth and home, as it were. Perhaps he is calling him out on it on purpose because he is tired. Perhaps it is simply within his nature. He really would rather that Norrell have sent Lucas instead. At least then he might have had some sympathy for his present situation and his aching head, instead of...well. This.