In four experiments with 4-, 6- and 9-year-old children and adults the hypothesis was tested that, with all other conditions equal, a novel and unusual event elicits stronger curiosity and exploratory behaviour if its suggested explanation involves an element of the supernatural than if it does not (the impossible over possible effect -- the I/P effect). Participants were shown an unusual phenomenon (a spontaneous disintegration of a physical object in an apparently empty box) framed in the context of either magical (the impossible event) or scientific (the possible event) explanations. In the verbal trial, participants showed full understanding of the difference between the effect of genuine magic and the effect of a trick. In the behavioural trial, both children and adults showed the I/P effect. They were more likely to run the risk of losing a valuable object in order to explore the impossible event than the possible event. Follow up experiments showed that the I/P effect can not be explained as an artifact of the different degrees of cost of exploratory behaviour in the possible and impossible conditions, or as a result of misinterpreting magic as tricks. The I/P effect emerged when the cost of exploratory behaviour was moderate, and disappeared when the cost was perceived as too high or too low.