I'm wondering about how dangerous it would be to have a razor blade in the mouth during a scene - like on top of the tongue, then closing the mouth. There'd be a strong instinct to do anything possible not to swallow it, but I'm concerned with the risk of accidental reaction such as sneezing, getting a swallow reflex from something, fear building and causing temporary panic, or other problems. Holding it between the teeth should make it pretty difficult to go wrong, but would you say this is just too risky to experiment with? There'd be medical equipment and someone trained as a nurse/paramedic, just in case. As a safer alternative, what about a knife, with a wide hilt that would make it impossible to go too far in.