It's produced mainly by the corrugator muscle, which lowers & pulls together the eyebrows
- Paul Ekman [PAR] consonant produced at the level of the larynx; but as laughter is not "speech" we 
... control over its expression; the laughing person has been described as ... of 
subjects mainly refer to the awareness of the impulse to laugh, spontaneous ..... 
regions of the forehead; 3=corrugator supercilii-draws the brows together and 
down-.