眼神(yǎn shén) - look in the eyes, expression of the eyes in Mandarin

眼神 (yǎn shén) is the expression in somebody's eyes, the thing you read off a face before anyone has spoken. Chinese uses it far more readily than English uses any single equivalent, which is why it turns up in every novel, every film review and most arguments about whether someone was being sincere.

It takes descriptive adjectives directly: 眼神很冷, 眼神很温柔, 眼神很奇怪. It also works instrumentally with 用, as in 用眼神 to communicate by look alone, and colloquially 眼神不好 means poor eyesight rather than a poor expression.

The trap is confusing it with 眼睛 and 表情. 眼睛 is the physical organ, so 她的眼睛很大 is about the shape of her eyes, not her mood. 表情 is the expression of the whole face. 眼神 is narrower and more intimate than either, and there is no tidy English noun for it, which is exactly why it is worth learning as a unit rather than translating.