Approximately 141 million Valentine's Day cards are exchanged worldwide every year.
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Couples' personalities converge over time to make partners more and more similar.
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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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There's a love mattress that is specifically designed for couples who sleep on each other's arms.
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A Korean man called Lee Jin-gyu fell in love with his large, huggable pillow and married it.
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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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In 2011, archaeologists discovered the skeletal remains of a Roman couple who have been holding hands for 1,500 years.
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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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