It is a well known and easily demonstrated scientific fact that different people sound different vowels when laughing, from which fact a close observer has drawn the following conclusions: People who laugh in A (pronounced as ah) are frank, honest, and fond of noise and excitement, though they are often of a versatile and fickle disposition. Laughter in E (pronounced as ay) is peculiar to phlegmatic and melancholy persons. Those who laugh in I (pronounced as ee) are children or simple-minded, obliging, affectionate, timid, and undecided people. To laugh in O indicates generosity and daring. Avoid if possible all those who laugh in U, as they are wholly devoid of principle.

— Henry Williams, A Book of Curious Facts, 1903