Don’t take your snake on the subway.

That’s what Melissa Moorhouse of Allston, Mass. discovered after her three-foot boa slithered away from under her scarf and around her neck on the Red Line between the Broadway and Andrew stations in Boston.

Penelope the snake was discovered two weeks later in a subway car at the JFK/UMass station.

The Massachusetts Bay Transportation Authority decided it had to do a special sanitizing of the car to reduce the risk of salmonella, and then sent Moorhouse a cleaning bill of $650.