Have you ever been forced to pretend a smile somewhere? Well, studies say that if you are forced to smile you will actually find the place or event more enjoyable. In 1989, Charles Darwin came up with a theory known as 'Facial feedback hypothesis' saying that blood vessels in the face feed back temperature information in the brain,altering our experience of emotions. I thought this was really interesting because at my work for instance, I have to always be smiling and laughing, so on days when i'm tired and crabby I am still forced to smile which automatically makes me have a way better time. In the end, smiles become conditioned stimuli for happiness and frowns become conditioned stimuli for unhappiness.