Oh, I definitely want to avoid giving it enough projection to provide a Reach bonus.
Blood claws, spikes, or short blades, though preferably running parallel to the body, would work. I'm not in favor of a blood katana or something like that. I guess it would work, and it emphasizes the powers inherent in Threats that aren't available to PCs, but ... YMMV.
Don't forget elemental effects, too (Generally, treat as Water).