How does Percy lull chauvelin into a false sense of security?

The meeting between Chauvelin and Percy is understandably awkward, and Chauvelin realizes he needs time before Degas returns with the men to arrest Blakeney. Meanwhile, Lady Blakeney watches from the stairwell, horrified. Percy, nonplussed, eats his dinner, and asks Chauvelin trivial questions; the Frenchman gets ever more eager for his henchmen to arrive.

Percy innocently asks Chauvelin if he would like to inhale a top-notch brand of snuff he acquired from abroad. Chauvelin falls for the trap, ends up inhaling pepper, and Percy calmly leaves the room as Chauvelin struggles -- just before the soldiers arrive.