5 Most Incredible Discoveries of the Week

A Death Valley mystery potentially solved and a strange revelation about Hello Kitty make the list:

• Death Valley's Moving Rock Puzzle Finally Cracked: For at least a century, the "slithering stones" of Death Valley—rocks, some of them boulders weighing more than 600 pounds, that move across the desert floor and leave long trails behind them—have presented a puzzle, and researchers have been trying to solve it since 1948. Looks like they've finally figured out what's going on, and, weirdly, it involves ice.
• Hello Kitty Isn't Exactly a Cat: She may sport what appear to be whisker lines across her expressionless face, but Sanrio's iconic Hello Kitty may not be a cat. She also isn't a human, but she is a third-grade girl. Wait, what?

• Man Finds Giant Wasps' Nest in Bed: A British man visiting his mother discovered her spare bedroom was already in use—by thousands of wasps that had chewed up the mattress and pillows to make a 3-foot-wide nest on the bed. A pest controller says a small window in the bedroom had been left open and the wasps had been at work for at least three months.
• Science Explains Why Mozzarella Is Best for Pizza: In what sounds like the best middle school science project ever, mozzarella has been put to the test against several other cheeses on pizza and declared the best. Scientists in New Zealand used fancy cameras and software to study the way cheeses behave when cooked—and there's a simple explanation why mozzarella is the cheese of choice.
• Fluoride Levels in Our Water Could Be Making Us Dumber: The CDC says adding fluoride to our water supply is one of the biggest public health triumphs of the 20th century, but it seems that not only can too much fluoride damage our teeth and weaken our bones—studies in China and Iran appear to link excessive fluoride to a seven-point reduction in children's IQs.

Click for more discoveries, including what "gourmet" food cavemen ate 30,000 years ago. (More discoveries stories.)