Brain.

Oddee has a list of "10 Mind-Blowing Facts About The Brain" ...

7. "Inception" is Real

It turns out, there is something called Lucid Dreaming, where a person could control the outcome of a dream while in a sleep-like state. It has its roots in ancient Tibetian Buddhism, where aspirants would practice “Dream Yoga” – doing incredible feats of dexterity during sleep, reminding themselves of the illusory nature of existence. The term was first coined by Frederik (Willem) van Eeden in the 1880s, but the concept didn't take hold until the late 1960s. Nowadays, Lucid Dreaming is all the rage, with plenty of resources online to begin the training process.

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