[ Honestly, this whole interaction is probably red flags galore for both of them. He isn't helping his own case much by taking her grotesque carving in stride as well as the question. ]

Alcohol. It shouldn't damage the mechanism, and it'll double as a decent disinfectant. Though it might not be the best option for getting the blood out.

[ Of course, the best options aren't readily available, in these circumstances. So maybe that's not such an important factor. ]