QUESTION: hey im sure you have already answered this before but i was wondering what is the blood groove on swords actually used for? is it cosmetic or for structural stability, or maybe just for blood letting? thanks
ANSWER: Just about every culture that uses swords has one with a blood groove - which is properly called a 'fuller' (or bo-hi/hi for Japanese swords).The reason is to reduce the weight of the sword a little and change the point of balance, generally resulting in a faster and lighter sword without losing too much in the way of structural intergrity (it acts much like an 'I-beam' does as used in the construction industry).
There are rumours and myths that it was used as a channel to let the blood run off the sword or to help prevent suction from a thrust trapping the blade if it was stuck into an opponents gut, but the reality is - it was used to get just a little more speed and agility into the blade, because when people actually used to fight with swords in the past, any advantage can be the difference between life and death...
Oh, and also - as a bonus, it does look cool! ^_^
Hope this helps.