Flick knife is a spring-loaded knife. Push the button forward to pull the spring, which is hooked on the blade through a pin. Since the blade is locked by a card at this time, the spring stretches and stores energy. Continue to push the button forward, the card is pressed down by the button, and the blade is suddenly released. Under the action of the spring elastic force, the knife handle pops out and relies on inertia to press down another card, and it is locked again. Pushing the button backwards is the opposite. The other is a rotating jump knife, in which the blade can only rotate and jump out, but cannot retract.