Young children show sensitivity to others’ emotions, discriminating between facial expressions and using them to help guide their behavior. Beyond providing information about how others are feel- ing, emotional expressions also can support inferences about the non-social world. Here, in four experiments, we investigated 18- to 28-month-old children’s ability to use others’ emotional responses to reason about physical objects. We found that 24- to 26-month-old children successfully used an agent’s incongruent emotional responses (‘‘Yay! Yuck!”), but not congruent emotional responses (‘‘Yay! Wow!”) to infer the presence of multiple hidden objects (Experiment 1). When two different agents produced the incongruent emotional responses, children did not infer that multi- ple objects must be present (Experiment 2), implicating early recog- nition that different people can have different emotional reactions towards the same entity. Younger, 20-month-old children failed to use incongruent emotional responses to make inferences about hidden objects (Experiment 3), although they succeeded at using contrasting words in an otherwise identical task (‘‘A blick! A fep!”; Experiment 4). These results show that young children can use other people’s emotional responses to reason about the physical world—an ability that develops in the second year of life.