Spy movies frequently feature a suicide pill, which a spy would ingest if caught, preferring to die than being interrogated by the enemy.
Could martial arts be used to the same effect? E.g., imagine a martial arts expert who was a spy is captured and placed by the enemy in a room where he has no weapons. Suppose, even, it's a special room adapted to hold those who're a suicide risk, e.g., no hard walls (maybe whatever they use in psychiatric hospitals). Suppose also the spy is stripped naked, but he isn't tied up.
What could a martial arts expert who was a spy do in these circumstances to kill himself effectively, without using any devices or substances but his own body, and a few long minutes to spare while no one's watching?