A "Pabst Trap" is a series of empty beer cans, typically Pabst Blue Ribbon, strung together with fishing line and set across a low-speed roadway at night. Typical Pabst Trap catches include vehicles, bicyclists, and drunk Navajos.
The man stopped and exited his car, examined the cause of clamour, and exclaimed: "Oh! It's a Pabst Trap!" before returning to his vehicle.