Charcoal, mist, like something insubstantial. The wispy tendrils have nearly nothing of blood left in them, but that they're coming from an injury; they stop rising only when they hit the upside-down bottom of the vial, curling like true smoke.

Stocke inclines his head, acknowledging; he waits until the smoke in the vial's progressed from a muzzy gray to entirely opaque black, then stoppers it - still upside down - with a finger while he reaches for a cork.

Once it's sealed and flipped right side up, he holds it out to Rin.

He doesn't bother covering his still slowly "bleeding" arm, dropped back down to his side - though without a container holding it in, the smoke dissipates quickly. Maybe there's nothing to do with that but wait? Can't really slap a band-aid on it; that's not airtight.