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The startle has a side effect that has nothing to do with self-protection: It broadcasts personal information well beyond the simple fact that you are startled. The reason is that your moods and thoughts strongly influence how your startle reflex manifests itself in any given moment.
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Another creature, watching your startle reaction, could in principle learn a great deal about your inner state—and use that information to its advantage. Are you confident or anxious? More likely to run away, or more likely to go on the attack? Are you dominant over the people around you, or do you feel frightened by them?
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The startle reflex is not, itself, a social gesture. It’s not a smile, a laugh, or a frown. It’s simply a reflex that evolved to protect the body. But it puts you at risk, too. By leaking signs about your inner state to the rest of the world, it becomes an exploitable data breach.
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