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The sight of blood can be hard on anyone, but there are some who are squeamish enough to faint at the very sight of it. Some may consider such people faint-hearted, but there are reasons for this oddly dramatic response – which isn’t as uncommon as one may think it is.

This behaviour is often classified as blood injury phobia. And it works in strange ways, as the video by BrainStuff above will tell you. For instance, donating blood, getting an injection, or bleeding from an injury make many uneasy. But a person who faints at the sight of blood may not show the same response to cutting themselves.

Host Josh Clark says the fainting spells are a result of anxiety, where the blood pressure spikes suddenly and then plummets just as quickly, causing the blood to drain from the brain. Why does this happen? Watch the video to find out.

And does fainting at the sight of blood go back to evolution? Researchers have been trying to make sense of such a connection for a long time now. One theory traces this behaviour to the caveman’s attempt to play dead to ward off predators. Speaking of predators, even goats faint as a survival strategy.

Is that what it is all about then – fight or flight, or in this case, fight or faint?