Most people think of MRIs, or magnetic resonance imaging, as being pretty terrible—after all, you're basically lying in a tube while a big machine takes photos of your insides. But those resulting pictures are pretty amazing and can be used to spot tumors, organ abnormalities, and even breast cancer.

And sometimes researchers use MRIs to take a look at something even more mind-blowing—like two people having sex. That's one of the crazy clips shown in a new video from Vox.com, which pieces together amazing MRI footage of the body in motion, from kissing and talking to birth, and yes, sex.

That particular part of the footage came from a 1999 study in the British Medical Journal, which proved that you could actually use an MRI to record images of couples having sex (for research purposes of course). Plus, they discovered that the penis makes kind of a boomerang shape during missionary position. We'd call that a worthwhile study.

Check out the full video below. Warning: It's a little NSFW around the 0:49 mark.

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