You are hiking in the mountains when, out of the corner of your eye, you see something suspiciously snakelike. You freeze and look more carefully, this time identifying the source of your terror: a stick.
Yet you could have sworn it was a snake.
The brain may play tricks, but in this case it was actually doing you a favor. The context — a mountain trail — was right for a snake. So your brain was primed to see one. And the stick was sufficiently snakelike to make your brain jump to a visual conclusion.
But it turns out emotions are involved here, too. A fear of snakes means that given an overwhelming number of items to look at — rocks, shrubs, a hiking buddy — “snake” would take precedence.
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