User blog comment:Neowitch/686 - You're hot when you're cold/@comment-4754162-20121024105219/@comment-3425840-20121024111100

Either Zoro does not have BH implying Luffy said about KH or HH when he was talking to Law (a weird case as the context was fighting Caesar, a Logia user thus BH is the one expected). Or he is not using it. The reason maybe that Zoro wants to fight with pure swordsmanship.

Another possibility might be that you need to learn how to put Haki to weapons and Zoro has yet to learn that and he does not want to leave the swords and go in a fist brawl.