Historically, sweat has been an active ingredient in perfume and love potions.
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Parents receive 1 out of every 5 Valentines.
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Couples' personalities converge over time to make partners more and more similar.
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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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Ten seconds of hugging a day increases levels of oxytocin, which can reduce blood pressure, thus cutting the risk of heart disease.
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If you mouth the word "colorful" to someone, it looks like you are saying "I love you".
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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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When you are looking at someone you love, your pupils dilate, they do the same when you are looking at someone you hate.
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