A great deal of what we know about the world has not been learned via first-hand observation but thanks to others' testimony. A crucial issue is to know which kind of cues people use to evaluate information provided by others. In this context, recent studies in adults and children underline that informants' facial expressions could play an essential role. To test the importance of the other's emotions in vocabulary learning, we used two avatars expressing happiness, anger or neutral emotions when proposing different verbal labels for an unknown object. Experiment 1 revealed that adult participants were significantly more likely than chance to choose the label suggested by the avatar displaying a happy face over the label suggested by the avatar displaying an angry face. Experiment 2 extended these results by showing that both adults and children as young as 3 years old showed this effect. These data suggest that decision making concerning newly acquired information depends on informant's expressions of emotions, a finding that is consistent with the idea that behavioural intents have facial signatures that can be used to detect another's intention to cooperate.