An involuntary expression of merriment and pleasure; it includes the patterned motor responses as well as the inarticulate vocalization.
Wit and Humor as Topic
The faculty of expressing the amusing, clever, or comical or the keen perception and cleverly apt expression of connections between ideas that awaken amusement and pleasure. (From Random House Unabridged Dictionary, 2d ed)
Laughter Therapy
Therapeutic use of humor and laughter to improve emotional well being and health.
Smiling
A facial expression which may denote feelings of pleasure, affection, amusement, etc.
Crying
To utter an inarticulate, characteristic sound in order to communicate or express a feeling, or desire for attention.