A good, real, unrestrained, hearty laugh is a sort of glorified internal massage, performed rapidly and automatically. It manipulates and revitalizes corners and unexplored crannies of the system that are unresponsive to most other exercise methods. – Author unknown, from an editorial in New-York Tribune, quoted in Quotations for

To promote laughter without joining in it greatly heightens the effect. – Honore de Balzac

Some men laugh habitually in falsetto…. We remember once to have heard a feminine laugh so painfully and regularly tuneful that it could literally have been reduced to musical notation. – “Laughter,” in The Spectator for the week ending Saturday, January 19, 1889