Standing next to someone's mood can be enough to catch it

People unconsciously mimic the facial expressions, postures and speech patterns of those nearby, and that mimicry feeds back into actually feeling the emotion on display. It's part of why one anxious or cheerful person in a room can measurably shift everyone else's mood without saying a word.

— Elaine Hatfield, John T. Cacioppo & Richard L. Rapson, Emotional Contagion — Cambridge University Press, 1994
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