There are a few people who can have lucid dreams at will. And the increase in induction techniques has provided many more subjects who have them frequently. This has opened the way to using lucid dreams to answer some of the most interesting questions about sleep and dreaming.

How long do dreams take? In the last century, Alfred Maury had a long and complicated dream that led to his being beheaded by a guillotine. He woke up terrified, and found that the headboard of his bed had fallen on his neck. From this, the story goes, he concluded that the whole dream had been created in the moment of awakening.