Nicholas himself has given in to the bull's challenge before. And he's not standing here now in some mistaken belief that he'll have better luck if he tries again. Sure, it was a nasty blow to his pride, but there are in fact some things more important than that.

For example, the reason he's approached this newcomer.

"Where," Nicholas asks without preamble, pointing at Vimes's cigar, "did ya get that?"

And were there also cigarettes there? Please tell him there are cigarettes in town again.