How many smells can a person discriminate? Bushdid et al. created mixtures comprising 10, 20 or 30 components from a collection of 128 different odorous molecules and asked participants to identify the 'odd-one-out' from three mixtures. Each participant completed 264 of these tests in order to find the average olfactory resolution; that is, the maximum percentage of components shared by two mixtures that could still be discriminated. They found that most individuals could discriminate between two mixtures sharing less than ∼52% of their components. The authors then worked out the number of hypothetical mixtures that were discriminable by an average person, which was more than a trillion (1.72 × 1012).