Ruby's Knife

The demon Ruby has a knife that acts much like the Colt revolver--it can kill amost anything, but it must be wielded in such a way that the wound it gives is the kind that would be fatal to a human. Thus, a minor cut is not fatal. More powerful demons are able to withstand more severe woundings by the knife. For example, Dean is unable to kill the powerful demon Alastair with the knife. Ultimately, the Winchester brothers kill Ruby with her own knife.