Sometimes a person will smile, but an observer notes that the person's eyes look sad. erving goffman would say the sad eyes are part of the expression the person:

erving goffman would say the sad eyes are part of the expression the person: gives off

according to Erving Goffman, out eyes are the most honest body parts that we have. He said this because Our brain that process all our emotion will directly send signal to our eyes as a form of response based on the experience that we feel (for example, if we're sad, our eyes will turn watery)