Here is some information from an article about smiling you need.
Main point: “Psychologists call this [type of smile] the ‘Duchenne smile,’ and most consider it the sole indicator of true enjoyment.”
Key points:
- “The intensity of a true grin can predict marital happiness, personal well-being, and even longevity.”
- “…researchers catalogued viewer reactions and found that Duchenne smiles correlated with the pleasant films.”
- “Mental health researchers soon noticed that wherever positive emotions went, Duchenne smiles followed.”
- “…genuine smiles are not transient sparks of emotion but rather clear windows into a person’s core disposition.”
Here is a video about what Duchenne smiles look like: