Childermass is hardly unfamiliar with the idea that people might not want to have him stick around for a chat. She wouldn't be the first person certainly. There are those that find his very presence vaguely unsettling, never mind recognizing him for the threat that he might very well be. Norrell may be a very powerful witch, but Childermass is nothing to shake a stick at, and he has a level-headedness to himself that his master will never even hope to attain.

"The sports hall?" he asks, raising an eyebrow at her suggestion. It's clear she would like to see the back of him, but he wants more. Why such a suggestion, and why to him? Is there anything behind it? Might he actually learn something from it. Might as well ask her straight out. Nothing better than learning information straight from the horse's mouth, as they say.