The invisible tail that Zoro totally wouldn't expect Imu to have... oh wait its flopping around everywhere lol.
Imu aint summers lil nephew. Zoro can know about his tail all he wants, he can't do shit about him. Sanji can't either, but the idea that "oh he KICKED sanji and he DIDNT USE A SWORD against zoro" means ANYTHING is a non sequitur that makes little sense. Either way, he put the same effort into destroying them: zilch