Recently I saw a video of someone who had been practicing draw cuts on falling fruit and he had ended up cutting himself very badly on his left hand. From the accompanying 'after' picture it looked like it needed a dozen stitches and as I watched the video again I cringed as I saw him stop his cut abruptly his face conveying the pain and him walking away clenching his fist. I've said before that if you're careful, then the most dangerous place for a swordsman is going to be the sharpening block where complacency can become a problem. It occurs to me now that maybe theres a close contender in nukitsuke.
The problem with this falling fruit practice is that you have to get the sword out of the saya very rapidly indeed in order to cut the fruit before it hits the floor. For this reason it's become a popular way of demonstrating some degree of skill amongst backyard cutters and some martial artists alike and it's also the thing that makes it potentially very dangerous. When you're trying to do something exceptionally fast, you run the risk of doing it with less focus. The cut becomes about the speed of the draw and not it's quality. Now I'm not belittling the skill of the person whose video I watched in any way in fact I've seen them perform this cut before with no problems. When you play with sharp things you run the risk of getting cut, it's just one of the risks that we're all aware of, but it does highlight how when you become almost obsessed with the end result you pay less attention to the component parts that make it. If you forget to add the sugar to a cake then it doesn't taste very nice but if you forget to check the safety on a rifle then the results could be far more catastrophic.
The way that the sword cut through the saya however happened the exact same way that it happens pretty much every time anyone cuts themselves during the draw. To understand why nukitsuke needs to be learnt with and shown the proper respect and care, I need to describe it really simply.
The sword and the saya are two seperate parts and when the sword is inside the saya completely, no amount of reasonable force is going to push the blade through it.
When you are drawing the sword, as it moves further out of the saya the pivotal point at the koiguchi and the distance between it and the tsuka turns it into a lever and any small amount of pressure on the tsuka will cause a comparatively massive amount of pressure through the blade and onto the side of the saya which will easily push it through the wood.
So if it isn't clear of the saya as you start to move the sword rapidly to the right then it will simply cut through the wood and into your hand.
Remember that the saya is traditionally made of a light and soft wood as well which makes it all the more easy for it to do this and leave you bleeding profusely.
There are saya that been made with this in mind and they have a harder wood insert on the Ha side of the saya up at the koiguchu and these offer a fair degree of protection. I believe that this is a modern modification but I could be wrong. Although this hard wood will protect against the occasional scuff and whoopsie, it is no replacement for simply being more attentive and moving slower. Always concentrate more on the draw than on the cut and you stand a better chance of coming out unscarred.
Be safe, people.