Recent studies have established that even infants can determine what others know based on previous visual experience. In the current study, we investigated whether 2-and 3-year-olds know what others know based on previous auditory experience. A child and an adult heard the sound of one object together, but only the child heard the sound of another (target) object. When later the sounds of both objects were played simultaneously, the adult reacted with surprise and excitement ("Oh, listen, what is that?"). In response, both 24-and 36-month-olds directed the adult's attention to the target more often than chance and more often than in a control condition in which the adult had heard neither sound. These results indicate that by 24 months of age, children's understanding of others' knowledge and ignorance is not limited to the visual domain but extends across perceptual domains.