His eyebrows flash when he sees you

It lasts about a fifth of a second — a quick, involuntary lift of both eyebrows the moment your eyes meet for the first time in an encounter. Anthropologists have documented this 'eyebrow flash' across every culture ever studied, which suggests it's one of the oldest social signals in the human repertoire. It means: I see you, and I'm glad you're here. The key word is involuntary — it happens below the threshold of conscious control. Most people never notice it because it happens so fast. But once you know to look for it, you can catch it reliably by watching someone's face in the half-second after they first register your arrival. It's particularly valuable because it's impossible to fake convincingly — attempts to perform it consciously look slightly off. If you see a genuine eyebrow flash when he spots you, you've bypassed all the polished social behavior that comes after and seen something honest.