Even monkeys and apes have some facial expressions that are similar to human smiles. It is possible that smiling, laughing and tickling are used to create bonds between babies and parents. When a parent tickles a baby and the baby responds with a smile or laugh, the parent laughs and smiles too. In this way, the baby and parent get to know one another and the baby learns all about laughter by watching and responding to a parent. Research has shown that laughing is more than just a person's voice and movement.
Laughter requires the coordination of many muscles throughout the body.
It may be a good way for people to relax since muscle tension is reduced after laughing. There are some cases when a good deep laugh may help people with respiratory problems by clearing mucus and aiding ventiliation. Perhaps laughing can also help cardiac patients by giving the heart a bit of a workout. Also, immediately after abdominal surgery, people should not laugh too hard because they could tear out their stitches accidentally. Care should also be used in patients with broken ribs.