text: You can read a friend's emotions to tell how they are feeling. If you have a friend is forcing herself to smile, you can tell she is feeling sad, depressed, or angry. I know you can't read someone's mind to tell how are they feeling. Only you can read someone's emotion is by the computer knownig your are sad or happy. An example in the article, "if you smile when a web ad appears on your screen,a similar ad might follow. But If you frown,the next ad will be different". This is how computer tell emotions on that person.