Hand clapping is a motor program mastered in infancy. Inspired by a question posed by an Eastchester High School AP Psychology class, we present a case series of 14 patients with hemispatial neglect who, when asked to clap, repeatedly performed one-handed motions stopping abruptly at the midline of the visual hemispace, as if pantomiming slapping an invisible board. In contrast, hemiplegic patients without neglect will reach across and clap against their plegic hands. This phenomenon provides an easy, rapid, and unambiguous test for neglect, applicable to patients of any ethnicity or age. Ann Neurol 2009;66:114-117.