The 2,000 mice that drifted to earth over Guam Sunday hung from tiny paper parachutes, attached to cardboard, which sounds absolutely adorable until you learn their deadly truth: The dead mice, infused with acetaminophen, were being used as bait to kill brown tree snakes, an invasive species threatening Guam’s birds. Apparently, the active ingredient in Tylenol kills the snakes even in very small doses, so presenting their favorite food stuffed with it makes for a good delivery system. Bit hard on the mice, though.