We do have a zeal for laughter in most situations, give or take a dentist.

The line plays on the idea that people are generally eager to find humor—even in difficult circumstances—while conceding a comic exception: the dentist’s chair, a near-universal site of anxiety and discomfort. Heller’s wit hinges on deflating a broad, almost philosophical claim (“a zeal for laughter”) with a mundane, bodily reality that resists levity. The effect is characteristic of his darkly comic sensibility: laughter is presented less as carefree joy than as a coping mechanism, one that falters when pain or vulnerability becomes too immediate. The phrasing also suggests a skeptical view of grand statements, undercut by everyday experience.