Watch out! How a fearful face adds credibility to warnings of danger

People display facial expressions of fear to communicate danger to others and sometimes to exaggerate danger to manipulate an audience. Here we test whether fear expressions add credibility to a speaker's warnings of danger. Participants played an incentivized lie detection game in which they guess whether a confederate partner is lying or telling the truth. Participants viewed a video of their partner's message, after reading that there was a good chance (75%) their partner was instructed to lie. We manipulated across conditions whether the partner stated the message with a neutral or fearful expression. Experiment 1 finds that participants were more likely to believe the speaker's warning of danger when it was conveyed with a fear expression compared to a neutral expression. Experiment 2 finds that when a speaker instead claimed that a danger was absent, a fearful expression no longer added credibility to their message. These findings provide evidence that fear expressions add credibility to statements of danger, specifically, rather than any claim.