Scientists may have uncovered a way to track the ever-evolving flu virus buried in 10-year-old snot. In an effort to understand how the flu virus rapidly mutates — which leaves scientists constantly scrambling to come up with a new flu vaccine — researchers decided to study four cancer patients' snot, which had been collected a decade ago and frozen. Because cancer patients tend to come down with the flu for a longer period of time than healthy individuals, the scientists had a longer window of time to observe the mutating virus.