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Surprise vs Startle Reflex

You've come back from market and about to enter in your home - the only place in this whole world which entirely belongs to you and your family. You don't feel not that tense or cautious as you use to be in outside world from where you're returning to your 'own cave'. You see that front door is partly open but nobody seems inside the house while looking through it from a long distance. What's the exact matter? Has anything gone wrong? Where are other family members? You're completely unaware about what is about to happen within few seconds from now. You keep moving on towards the door.

In desperation, you decide to enter in your house to check if somebody has broken in it with evil intentions. As you enter through the partly open door, somebody else welcomes you in an unexpected way. Your naughty child appears in front of you from behind the same door in no time, poses both of his hands as claws and loudly roars like a tiger. You abruptly shake from tip to toe, palms of you hand open up suddenly, your hands come closer to your face, muscles of your neck become tight and your squint your eyes. You cannot do anything but only watch your kid laughing at you.

You momentarily feel as if you have received an electric shock by accident or your kid given it to you. This automatic response of our body seems to last within fractions of a second. Is it a short-lasting expression of surprise or shock that your child wanted to give you, by coming from behind the door suddenly? What it could be? Most of the people assume an uncontrolled and sudden response of body as emotional expression of either fear or surprise. Scientifically, it's none of the both. This response is called as Startle Reflex. All over the world, naughty kids startle others to make fun of them.

Startling reflex is very primitive neuro-physical response evolved to cope up with suddenly appearing signs of dangers. Startling is neither being afraid nor surprised but just an unsophisticated defensive movement made by brain. Body shakes or wobbles instantaneously to avoid being caught or harmed by an entity that’s not fully understood at given moment. It includes unexpected or sudden sound, touch and trespassing. You may easily watch a sleeping infant showing startle response after receiving touch or listening loud sound. Just go through first 5 seconds only of this clip (below).


Startling of our body lasts over few milliseconds only. Unlike expressing fear or surprise, our body couldn’t react systematically upon instantaneously obtained sensory experiences (stimulus). In fact, startle reflex might have lead to evolution of both fear and surprise in mammals - the group of creatures that we belong to. Reflexes are pre-determined autonomous behavioral strategies that evolved before emotions. So what is the difference between startle reflex and surprise then? Let's try to find out from body language clues.

If we pay close attention at facial expressions of surprise then we can easily find the difference. While expressing surprise, our eyes remain wide open, eyebrows arch upward, mouth opens and jaw is dropped. By doing so, our brain tries to collect more and more visual clues from the entity which is drawing our overwhelming attention. Most important thing is that our eyes need to remain open to receive clues and express surprise about them. In case of startle reflex, it is not basically required that our eyes should remain open. Just listening to an abrupt and loud should is enough for our brain to make us shake.

Related Articles:
1) Fear Factor 2) Turtle Effect: Body response under threat 3) The Body Seeking Comfort