rictus
noun [ C ] uk/ˈrɪk.təs/ us/ˈrɪk.təs/
龇牙咧嘴
an expression in which someone shows their teeth in a smile, but looks strange or in pain rather than looking happy and relaxed
When I mentioned her name, his wide smile stiffened into a rictus. 当我提起她的名字时，他的微笑变得僵硬起来，成了龇牙咧嘴。