Quote Originally Posted by RyougaZell
I was wondering the same.
I think he spilled the blood on the weapon and then 1) self injured himself or 2) spilled some of the same blood on his face
i dont think so... kakashi got the blood from kakuzu because of raikiri then passed it to shikamaru, then when hidan "slashed" shika he actually failed and shika threw the pill with blood to the scythe and then he used a needle (you can see it in one of the last pages) to scratch himself