Sonograms have been used in the United States since the 1940s, and provide doctors with a noninvasive way to peek inside the human body. A sonogram works by sending out sound waves that are too high-pitched to be heard by human ears, which create an internal image, most often of infants still in their mother's womb. All expecting mothers are advised to have at least one routine sonogram to check on their baby's overall health, size, and formation. Although sonograms are commonly used in medicine, comedian Jimmy Kimmel's Aunt Chippy was one American who had never seen one in action. When her daughter Micki became pregnant with her first child, Jimmy and his camera crew knew they had the chance to create the prank of a lifetime.