Every year around 1 billion Valentine cards are sent. After Christmas it's a single largest seasonal card-sending occasion.
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When you fall in love, that 'high' feeling is caused by a flood of dopamine that is similar to that of cocaine.
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In Finland, Valentine's Day is called "Ystävänpäivä" which translates into "Friend's day".
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Wearing red increases attraction.
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Couples' personalities converge over time to make partners more and more similar.
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Historically, sweat has been an active ingredient in perfume and love potions.
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In Korea, if you do not receive any gift on Valentine's day then all the singles go to Korean restaurants and eat black noodles to celebrate (or mourn) their single status.
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In 2011, archaeologists discovered the skeletal remains of a Roman couple who have been holding hands for 1,500 years.
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