first of all, any questions along the lines of WHAT? WHY? HOW COME? WHAT THE HECK? will be totally ignored and NOT be answered.
there is a story behind this. a story i will not tell you just yet, but once you know what the story is, you'll know why zoro is all sweating, why franky is being the idiot that he is, and why vivi seems to be infatuated by zoro.
and no, this is NOT zoroxvivi <_<