@Ned_Gutters:
Maybe I saw an espcially bad translation, but didn't trebll call the move "Jigsaw"? That would imply an uneven, puzzle-piece like cut.
Saw just implies the motion, I think. Dofla moving his leg back and forward to cut Law's arm, instead of doing it with one swipe.
Even with a normal saw it's a lot easier to make a straight clean cut than an uneven one. If you ever used a saw for wood or something, you'll probably get what I mean.
But ultimately, I don't think the way the arm was cut is ever going to be an issue.