Wrinkles should merely indicate where smiles have been. – Mark Twain, Following the Equator

Smile. Have you ever noticed how easily puppies make human friends? Yet all they do is wag their tails and fall over. – Walter Anderson, The Confidence Course, 1997

Smile! It increases your face value. – Robert Harling, Steel Magnolias

[A] smile is hovering about her lips, as if some playful speech were awaiting the right hearer. – George Eliot, “Another Love-Scene,” The Mill on the Floss, 1860