Micro-expressions mean that people express their inner feelings to each other by making some expressions. Between different expressions made by people or in a certain expression, the face will "leak" other information. The shortest-lasting micro-expressions can last 1 / 25 seconds, although a subconscious expression may only last for a moment, it is easy to expose emotions. When the face is making an expression, these extremely short-term expressions suddenly flash by, and sometimes the opposite mood. According to the above definition, which of the following is a micro-expression? ['The sales clerk may flash a contemptuous smirk when he smiles in front of a shabby customer.', 'The spy sends a message to associates in the blink of an eye.', 'After Wang was frightened, his face continued to twitch.', "Walking against the biting cold wind, Xiao Li's upper and lower teeth kept shaking and colliding."]