The US has dropped 2,000 dead mice over Guam in an effort to curb the Pacific island's growing population of invasive snakes.
The mice are stuffed with 80mg of paracetamol, the mild pain medication, which is deadly to brown tree snakes.
The rodents were tied to miniature cardboard parachutes designed to land in branches, where the tree-climbing snakes could easily find them.
Sunday's drop was the fourth aerial delivery of mice to Guam this year.
The programme has cost the United States $8m (£4.8m) annually.
Guam, a US territory, has been an important US military outpost since World War Two.
The brown tree snake, native to northern Australia and Papua New Guinea, first arrived on the island after the war, probably aboard a cargo ship, according to the US geological survey.
Since then, the population has boomed due to abundant prey and few natural predators.
US scientists put the snake population at three million, with some areas containing 13,000 snakes per sq mile.
The snakes are threatening native exotic bird species, as well as costing the Guam Power Authority up to $4m annually in repair costs because they sneak into power stations and cause outages.
US Department of Agriculture (USDA) biologist Dan Vice told the Associated Press news agency the aerial bait may be the best method to combat the snakes without harming other animals.
"The risk to non-targets is slight," Mr Vice said. "It would take 500 baits to kill a pig [and] 15 baits to kill a cat."
The USDA will track the results of the mission through tiny radio devices packed in some of the rodents.
"If it proves to be successful, then we may potentially start ramping up the efforts and doing this on a larger basis across more of Guam," Mr Vice said.
Fears remain that the snakes could migrate to Hawaii, where Mr Vice says their presence could be devastating.
Guam ports currently use specially trained snake-sniffing dogs to detect stowaways.