Refers to Nancy comic strip artist Ernie Bushmiller's penchant for, whenever some rocks seemed called for in the background, always drawing three rocks. The Zen-like nature of the Three Rocks are a subject of endless fascination for several notable comics artists and Nancy fans including Bill Griffith, Art Spiegelman, and Scott McCloud. As McCloud says in his rules for the card game "5-Card Nancy":

"Art Spiegelman explains how a drawing of three rocks in a background scene was Ernie's way of showing us there were some rocks in the background. It was always three. Why? Because two rocks wouldn't be 'some rocks.' Two rocks would be a pair of rocks. And four rocks was unacceptable because four rocks would indicate 'some rocks' BUT IT WOULD BE ONE ROCK MORE THAN WAS NECESSARY TO CONVEY THE IDEA OF 'SOME ROCKS.'"