Maggots can heal wounds. Yawns are contagious. Laughter can keep the doctor away. Perhaps you've heard some of these before and have seriously doubted their verity. Is it possible, though, that they really are true? Read on for five of the strangest—yet truest—health facts:

  1. Drinking too much water can be harmful. A healthy kidney can process anywhere from three-quarters to one liter of water per hour. If you consume more than that, though, you risk a dangerous shift in your electrolyte balance, known as hyponatremia. The excess water in your blood begins to enter your cells, which is harmful to the brain because cells have little or no room to expand. Brain swelling can ensue, leading to seizures, coma, respiratory arrest, and even death. Water intoxication occurs rarely—about 300 cases are reported in the United States each year—but it can be a particular concern to marathon runners (intense physical exertion causes the body to release vasopressin, an antidiuretic hormone that instructs the kidneys to conserve water), children, and those with illnesses that affect electrolyte balance.

  2. A hearty laugh a day can keep the doctor away. In 2005, researchers at the University of Maryland School of Medicine reported that after patients in the study were shown segments of a funny film, the inner lining of their blood vessels expanded an average of 22 percent. Such dilation plays an important role in improving cardiovascular health and overall well-being.

  3. Maggots and leeches are good for you. For years, maggots and leeches have been used for medicinal purposes. They fell into disfavor with the rise of pharmaceuticals, but in 2004, they became FDA-approved medical "devices." Despite the pharmacological and technological advances that have been made, nothing seems to match the way leeches can promote circulation (especially in the damaged veins of reattached limbs) and the ability maggots possess to remove dead cells from seriously infected wounds.

  4. Yawns are contagious. Well, at least 40 to 60 percent of the time. Scientists remain puzzled as to why this phenomenon occurs, though some theorize that it might have originated from a time when we used visual rather than verbal cues to coordinate social behavior. And yawns can be passed not only from human to human but from human to canine as well: A study published in the August issue of Biology Letters showed that when a man yawned in front of a group of dogs, 72 percent of them responded in kind.

  5. Men can get breast cancer, too. Although breast cancer in men is 100 times less likely than it is in women, 2008 will bring an estimated 1,990 new cases of male breast cancer in the United States, according to the American Cancer Society. Men and women are derived from the same blueprint, but varying hormones and hormonal levels augment and diminish different body parts. So while a woman will develop breasts, a man will not. Yet he still has the ducts and tissue that she has, and they are subject to cancer, especially if the man has a higher-than-normal estrogen level due to heredity, disease, or environmental exposure.