Let’s say you meet a man named John. If you had friends in common, you might use their opinions to judge his moral character. (If someone says, “I know John and he’s a liar and a cheat,” for example, you might tread carefully.) But if you know nothing about him, this new study indicates, your brain uses unconscious clues to determine his trustworthiness. Specifically, you’ll unknowingly analyze John’s face and compare it to other faces you’ve seen before. If John looks, on the whole, like someone you know who you deem trustworthy, you and John could become fast friends. But if John looks like someone who’s crossed you before, the opposite could be true.