Consider that you are watching a comedy film for the first time, you watched it completely having laugh so many times. Now, you watched it for the 2nd time, and this time you didn't laugh much and you watched it for the 3rd time and you didn't laugh at all; the humor became repetitive for you. Now say, you are watching a reaction video on YouTube for a particular comedy scene in that movie. And while watching the reaction, you find it comedy and you laugh on the same humor that was repetitive for you when you were watching it alone. We often does thing that are so much influence by others that we don't even realize it's happening. We tend to follow people's reaction, when present in a group of people. You laughed at the reaction video because there were people who were watching the film for the first time and they laughed and based on their reaction you Brain senses it and to prevent you from being "left-out" in the group, your Brain sends a signal to make you laugh, even it is NOT funny for you but still you laugh. From the Brain's perspective, say, you sitting with some people surrounded you and they are laughing out loud; no matter how hard you try you will eventually end up laughing along with them. Your brain will be like: "People are laughing, what's wrong with this guy, he ain't laughing" So your Brain ends up making you laugh. We, people, does so many things often, that are being influenced by the people around us, and we don't even know it's happening, as it happens "sub-consciously" and yet we feel like that we are in the control of ourselves. We have to realize, that we are not in the control of our body, it's the Mind and the Mind is not completely ours. Mind is something beyond any human can ever comprehend. THE ART OF LAUGHING.