This explains everything!
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The roots of close friendship extend far deeper than finding the same things funny and enjoying the same happy hour spot. According to the results of a study recently published in Nature Communications, the reason your best friends seem to just "get you" is likely due to the fact that their brain activity mirrors your own.

The study, conducted by a group of brain researchers and social psychologists at Dartmouth College looked at the brains of 42 students, and monitored their reactions as they watched old video clips. They watched America's Funniest Home Videos, footage of an astronaut at the International Space Station and a wedding ceremony, and observed vintage clips from CNN's Crossfire.

MRI scans showed that friends watching the same clips reacted in astonishingly similar ways. The same brain areas, particularly those associated with motivation, learning, affective processing, and memory, lit up in close friends. Furthermore, the closer the friends, the more similar their brain responses were. Researchers could even predict which participants were friends, based on their brain activity.

Their conclusion: people tend to be friends with individuals who see the world in a similar way.

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Professor Adam Kleinbaum, who co-authored the study, told Business Insider that it's unclear whether people are seeking out friends whose brains are already like theirs, or if friends change the ways their brains react to stimuli.

"We think both are happening," he noted.

The bottom line is: if it feels like your best friend can read your mind, she probably can.