(Potentially relevant link)

Bloodflick.

You've all had the experience: you've just killed a passer-by with your katana and now it's covered in blood. What to do? These things are, of course, quite difficult to clean, and leaving the blood on their is not an option. It will not only destroy the shine, but will cause corrosion.

Perform this simple manoeuvre! Hold the katana in your right hand, with the hilt close to your hip and the tip pointing down to your left. Slash into the air and watch the blood fly off in an incarnadine arc.

If you're lucky and well-skilled, your katana may now be safely sheathed without inviting damage to the blade or the noto. If not, you will still have to wipe if off.

You are now well on your way to being an Iaido master.. Use this skill only for good.