The Slow Mo Guys decided to see how sharp a katana is. To test this, they adopted the methodology of Man at Arms: slice through plastic bottles filled with water. They first cut through small water bottles full of water, and then they graduate up to larger bottles filled with soda or other colored liquids. Once the wielder gets the hang of things, he easily gets through them and describes it as cutting through butter. I only wish they would’ve put all the slow-motion clips at the end of the video if you just want to watch some very satisfying clips and don’t care about the setup.