Micro expressions occur when a person is trying to suppress or repress an emotion. The main points to remember are that micro expressions are:
当人试图压抑或隐藏情感时就会表现出微表情。有关微表情需要记住的两点为：

Brief
短暂

Micro-expressions can appear then disappear off the face in a fraction of a second. In other words micro-expressions occur so quickly, that most people don't even notice them.
微表情可以在一眨眼的工夫在脸上出现然后消失。换句话说，微表情出现的时间太短促，以至于大多数人甚至没有注意到。

Involuntary
不自觉

A micro-expression is caused by involuntary movements in facial muscles. Most people cannot control these involuntary muscles which are affected by their emotions.
面部肌肉的不自觉运动产生微表情。大多数人不能控制这些受自身情感影响的不随意肌肉。

Micro Expressions are generally grouped into seven universal emotions: anger, contempt, disgust, fear, happiness, sadness, and surprise.
微表情通常归为7类普遍情感：生气、轻蔑、厌恶、恐惧、高兴、伤心与惊讶。

anger
eyebrows down and together
eyes glare
narrowing of the lips
生气
双眉压低，挤在一起
瞪眼
嘴唇紧闭

contempt
lip corner tightened and raised on only one side of face
轻蔑
一边嘴角收紧上扬

disgust
nose wrinkling
upper lip raised
厌恶
皱鼻
上嘴唇上扬   摘自：英语学习技巧