The product is safe for humans but deadly for these snakes who are taking over 
the island and this way they can catch up with the snakes when they munch.
The snakes are wiping out bird populations on the island is not a native of the island but more than likely was brought here on ships or planes. It has no natural predators so the population just grows.
The dead mice also have radio transmitters so they can track the dead snakes to see if this method of attack works. BD
Dead mice packed with acetaminophen, strapped to pieces of cardboard and dropped from helicopters may help control one of the big headaches for the Pacific island of Guam – the brown tree snake.
The U.S. Department of Agriculture last week began dropping the expired rodents packed with 80 mg of the generic equivalent of Tylenol on the forests of Naval Base Guam.
Since scientists discovered that the household pain reliever was deadly to the brown tree snakes, they’ve been trying to figure out how to get it to where many of the serpents live in the canopies of the island’s forests, according to a report in Stars & Stripes. The Tylenol-loaded mice are attached to two pieces of cardboard joined by paper streamers that snake exterminators hope will catch on tree branches, providing deadly snacks for snakes at those heights, according to the Stripes report.
Tylenol-loaded mice dropped from air to control snakes – This Just In - CNN.com Blogs