THORNTON — A boa constrictor that escaped its cage and slithered down the block has cost its owner $50 in northern Iowa. Kevin Becker, 38, pleaded guilty Wednesday and was fined for keeping a dangerous animal in Thornton. A retired Iowa Natural Resources Department officer saw the snake in a yard a block or two from Becker’s home on Sept. 16. The retired officer grabbed it, put it in his pickup and called the Cerro Gordo County Sheriff’s Office.