But when the emotion that leads to stiffening the lip is more intense, and involves strong muscle tension, facial feedback may heighten emotional response.
但是当导致嘴唇僵硬的情绪变得更加强烈，并导致肌肉强烈绷紧时，面部表情反应就可能会增强情绪反应。
2
A litre of teacan contain up to 9mg of fluoride, which in excess can cause skeletal fluorosis, reducing bone quality and causing pain and stiffening of the ligaments.