How long does it take a baby to learn to laugh?

Research shows that smart babies are very sensitive to external things, and laughing is one of their greatest characteristics. Smart babies generally learn to laugh earlier and laugh more often. Judging from the baby's development process, the average baby learns to laugh in about 3 months. The baby's laughter can be divided into "innocent and happy effect" and "no one laughs". For example, when seeing the familiar faces, novel pictures or toys of mother or other close people, the baby will scream at the same time to show his smiling face by dancing. This kind of smile is called "innocent happiness effect". When the baby has enough to eat and drink and is in a good mental state, even if there is no external stimulus, the baby will smile involuntarily. This kind of laughter is called "nobody laughs". Studies have shown that the naive happiness effect is the first step for infants to communicate with others, a leap in intellectual development, a benign stimulus to brain development, and is known as the dawn of wisdom. As for no one laughing, it is still the psychological reaction after the baby's physiological needs are met. Both kinds of laughter are beneficial to brain development. Based on the above reasons, the researchers believe that if parents have more contact with their babies, they will also use happy expressions, language and toys to stimulate their babies to have an "innocent and happy effect" while ensuring that their babies have enough to eat and sleep and meet their various physiological needs, which will contribute to the development of their intelligence.