Presumably Flint's low Mm hummed across the lip of his cup stands in for 'You're welcome.' It is only half swallowed by his taking a nip of lukewarm ale. For just the barest moment afterward, it seems as if silence might lapse in over their corner of this crowded public house—this exchange already being somewhat more substantial than a simple question might have called for.

But:

"If you run into trouble, we can discuss it. It's not work that comes naturally to all men."