A traditional English proverb says, “The eyes are the window of the soul.” For this reason, it is no surprise that you do a lot to highlight our eyes. Between eye makeup, and the difficult choice between glasses or contacts, you spend a lot of time worrying about the way that other people will see your eyes.What makes your eyes so fascinating?QUIZ: Find Your Best Eye MakeupA key part of the eyes is the role that they play in the way you communicate. For one thing, your eyes say how you feel. If your eyes are wide open, you are generally interested, while if your eyes are more closed, you tend to be tired or bored. If you are sad or feeling ill, your eyes tend to be red. So, just the general state of your eyes tells other people a lot about how you’re feeling.And, if you compare the human eye to the eyes of our close animal cousin the chimpanzee, you can learn even more.If you look at the eyes of a chimp, the first thing you notice is that they are completely black. When you look at a chimp’s face, you have no idea where she is looking. It is impossible to follow a chimp’s gaze, because chimps do not have any white in their eyes.MORE: All About EyesThe human eye makes it possible to follow gaze. We see a lot of white around our eyes (the sclera), and then a colored iris and the black pupil in the center. The pupil is black because light goes into the eye and is captured by the light sensitive cells on the retina at the back and does not reflect back out.Because of the contrast between the color of the iris and the white of the sclera, it is easy to see what someone else is looking at. In fact, from a young age, we don’t really look at someone else’s eyes for long. Instead, we tend to follow the line of their gaze to see what they are looking at.This ability is quite important. When you’re cooperating with someone else, it is helpful to be able to look at the same thing they are so that both of you are focused on the same things in the world. Chimpanzees are more prone to compete with each other than to cooperate, and so it is not helpful for them to let others know where they are looking.MORE: What We Can Learn from ChimpsYour eyes also communicate interest. You tend to look at someone when you are interested in what they are talking about. When you are not interested, your eyes start gazing at other things in the room. That helps your conversation partners to get a sense of whether you are engaged in the conversation you are having together.Finally, your eyes do a lot to communicate attraction. People notice when you are looking at them, and that alone can make them feel good. In addition, when you find someone else attractive, your pupils tend to open up wider. Gazing at someone with those wide-open pupils is a clear sign that you find them attractive. So, even before you say it out loud, you’re already saying it with your eyes.Small wonder, then, that our eyes are such an important feature.MORE: How to Tell If Someone Likes You