After participating in traditional cannibalistic feasts intended to speed deceased loved ones' souls on their journey to the afterlife, many Papua New Guineans were struck down by kuru -- a strange, fatal affliction in which, among other symptoms, sufferers burst into uncontrollable laughter. Kuru was successfully eliminated, along with ritual cannibalism, but researchers are still studying the disease in a bid to learn more about neurodegenerative disorders such as Alzheimer's and Parkinson's.