Knife play

Running a knife or blade along the skin to induce fear, without actually cutting (unless blood play is also intended). Dull knives or back of blade often used. Psychological aspect is huge – the bottom’s adrenaline spikes thinking they might get cut. There’s also a trust element (they trust you won’t slip). If actually cutting, that crosses to blood play and requires extreme caution, sterilization, and aftercare for wounds. Many keep it at symbolic level (cold steel on skin, maybe cutting off clothes).