If you have no idea why someone would wake up from a coma speaking a foreign language, you’re not alone—scientists don’t know, either.

But it happens. In 2010, for example, a teenager awoke from a coma unable to speak her native Croatian, yet fully fluent in German. Though she had just begun learning German in school, it remains unclear how her brain cataloged enough of the language to allow her to speak it fluently, and why a coma prompted all that latent knowledge to spill forth.

It’s not the only thing scientists can’t explain. On this episode of The List Show, Mental Floss editor-in-chief Erin McCarthy is covering mysterious phenomena from around the world that our trusted experts are still trying to figure out. From Australia’s beautiful Morning Glory clouds to the eerie “upsweep sounds” in the Pacific Ocean, here’s what we know about what we don’t know.

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