Our Gemara brings a prooftext from the verse in Bereishis (43:34) that describes the gifts that Yosef gave to his brothers, and Binyamin, once they had reconciled:

וַיִּשָּׂ֨א מַשְׂאֹ֜ת מֵאֵ֣ת פָּנָיו֮ אֲלֵהֶם֒ וַתֵּ֜רֶב מַשְׂאַ֧ת בִּנְיָמִ֛ן מִמַּשְׂאֹ֥ת כֻּלָּ֖ם חָמֵ֣שׁ יָד֑וֹת וַיִּשְׁתּ֥וּ וַֽיִּשְׁכְּר֖וּ עִמּֽוֹ׃

Portions were served them from his table before him but Benjamin’s portion was several times that of anyone else. And they drank their fill with him.

The Maor VaShemesh (Rav Klonymos Kalman) comments on the verse, that the most significant gift that the brothers received from Yosef was actually, literally, מֵאֵ֣ת פָּנָיו֮, from his face.  He goes onto explain the value in seeing a tzaddik’s face and quotes the famous Gemara in Eruvin (13b), that Rabbi Yehuda HaNasi attributes his greater wisdom than his colleagues to having seen Rabbi Meir from behind, and had he seen his face, he would have been even wiser.

What can you see in a face?  Apparently quite a lot.  First of all, according to research which has been duplicated in many studies, there are seven basic human emotions which can be identified on the face.  These emotions are recognizable across language and cultures worldwide.  They are: anger, contempt, disgust, fear, joy, sadness, and surprise. 

( https://www.apa.org/science/about/psa/2011/05/facial-expressions )

Secondly, there are micro expressions, made famous by researcher Paul Ekman (2003, Emotions revealed. New York: Times Books.)  Essentially, he was able to prove through slow motion videos, that certain emotions that occur but are quickly repressed, or possibly unconscious emotions play out on a person’s face in less than a second.  There is a relatively small group within the general population who intuitively notice these expressions, while with training, people can learn to detect them.  

This skill does NOT allow you to read a person’s mind, as thoughts are not emotions.  However, in noticing incongruities between stated emotions, stated thoughts, and other micro-expressions, one can achieve something close to reading minds.  For example, when a person proclaims, “I am happy as can be”, but a micro-expression shows sadness.  You cannot say for sure he is lying, or exactly what he is thinking, but there is a feeling that seems to be leaking out that is the opposite of what he is saying.

So when you look at someone, or listen to someone, stop and really look. Take them in.