'X' became symbolic for a kiss because in the middle ages when alot of people were illiterate and they used to sign documents with an X and then kiss it for sincerity.
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Kissing releases masses of oxytocin, a "love potion" that helps couples bond and feel more attracted to each other.
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Wearing red increases attraction.
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When someone looks at a new love, the neural circuits that are usually associated with social judgment are suppressed.
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Historically, sweat has been an active ingredient in perfume and love potions.
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In medieval Italy, if a man was caught kissing a woman in public, he had to marry her whether he liked it or not.
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In 1999, a fisherman found a love letter in a bottle from a soldier in WWI. He returned said letter to the now deceased widows 86 year old daughter.
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Every year around 1 billion Valentine cards are sent. After Christmas it's a single largest seasonal card-sending occasion.
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