In American Sign Language, facial expressions are an important part of communication.
The facial expressions you use while doing a sign will affect the meaning of that sign.
For example, if you sign the word "quiet," and add an exaggerated or intense facial expression, you are telling your audience to be "very quiet."
This principle also works when making "interesting" into "very interesting," or "funny" into "very funny."
Facial expressions are an example of a set of behaviors called "non-manual markers." Non-manual markers include facial expressions, head tilt, head nod, head shake, shoulder raising, mouth morphemes, and other non-signed signals that influence the meaning of your signs.