Throughout history, people have used many methods to clean their teeth. Some ancient people chewed on frayed twigs. Others rubbed their teeth with cloth or swabbed them in vinegar. The Egyptians may have been the first people to use toothpaste when they mixed powdered pumice (a porous rock formed in volcanic eruptions) with vinegar and applied it to their teeth in the 100's B.C. Some toothpastes still contain pumice, but science has since supplied other toothpaste ingredients that the ancient Egyptians never dreamed existed.
What if there are colors within the visible spectrum that our brains can't perceive? In fact, there are. They're called impossible colors. But some researchers think they've discovered a way to see the impossible.
They stick around long after death and compete with the likes of Dracula, Frankenstein's monster and the Wolfman as one of the great figures of classic horror movies. Are you brave enough to unravel the history of these real-life, tangible ghosts?