It's actually true that you can change your mood by expressing the emotion that would normally follow a certain mood. You would expect laughter to always follow feeling joy, but the opposite can be done: you can act out laughing, and eventually you will feel better because of laughing. It's the reverse effect. There was a study in which groups of people watched the same film. One group had to keep a pencil in their mouth in a way the mouth would be when laughing. This group had the most positive reviews of the film in the category 'funny'.