Bitter smile face may be the manifestation of tetanus, may also be caused by the central nervous system excitation poisoning, but the probability of appearing is relatively low. 1. Tetanus: tetanus bacillus infection will release tetanus spasmodic toxin, the toxin first invades the facial muscles causing facial muscle spasm, it looks like a smile, but does not match with the patient’s inner thoughts, so it is known as the bitter smile face. 2. Central nervous system excitotoxicity: excessive central nervous system excitotoxicity drugs such as Niclosamide, Lobelin and caffeine can also invade the nerves and muscles of the face and cause a bitter smile. When patients are found to have a bitter smile, they should consult a doctor in time, ask whether they have a recent history of cuts or lacerations, or a history of taking central nervous system stimulant drugs, and improve the relevant examinations to standardize the treatment.