The muscles of the eyes help us detect if a smile is false or sincere.
When a person smiles, it can only be for two reasons, or is happy, or wants to appear happy. We will not wonder why we smile when we are happy, since it is a natural reaction to happiness and fun, however, there may be circumstances in which we have to resort to the other option, appear to be happy, content or having fun, either to dislike a boss who makes very bad jokes, so as not to interrupt a friend who is telling us one of "his stories", etc. etc.. Well, thanks to body language we can know through various gestures and expressions if a person is "appearing" to be happy, or on the contrary, if their happiness is sincere. Now, in particular, we will look at the eyelids and the muscles that surround the eyes. In the face there are two kinds of muscles that are used when we smile, some are called greater zygomatic and are those that pull the corners of the lips back and lift the cheeks, and the others are the orbicularis oculi that are responsible for moving and pulling the muscles around the eyes, partially covering them, stretching them or creating small wrinkles at their ends, which are crow's feet. I explain the names of these two sets of muscles because in practice they work independently and are the ones that could tell us if the smile is false or true. That is, the set of muscles formed by the greater zygomatics can be controlled consciously, so a person who consciously wants to appear happy, will use these muscles to tighten the lips and pull the corners of the mouth back to show the teeth and create a smile; however, orbicularis oculi are used unconsciously, resulting in a stretching of skin under the eyes, wrinkles at the edges and a slight sinking of the ends of the eyebrows. It may happen the case that someone uses the greater zygomatic muscles very intensely and raise the cheeks a lot, giving the feeling that the muscles around the eyes also move or wrinkle, so you have to pay close attention, when the smile is true, the eyelid falls slightly, the ends of the eyebrows sink down, and on the sides of the eyes wrinkles are created. This, of course, can be almost imperceptible in some people and in others be perfectly visible.