SUBARU OUTBACK WAS STARTED IN A PARKING LOT IN ORDER TO COOL INTERIOR DOWN. DRIVER EXITED VEHICLE AND WALKED BEHIND AND AROUND TO OTHER SIDE. DRIVE OPENED FRONT PASSENGER DOOR RETRIEVED AN ITEM AND CLOSED DOOR. DRIVER THEN WALKED AWAY A FEW YARDS IN ORDER TO PROVIDE WATER FOR A DOG. DRIVER HEARD A LOUD CRASH AND TURNED AROUND TO FIND CAR HAD ROLLED BACKWARDS OUT OF PARKING SPOT AND HIT A VEHICLE PARKED BEHIND IT. CAR WAS STILL RUNNING AND FOUND TO BE IN REVERSE. NO ONE WAS IN EITHER CAR AND NO INJURIES. BOTH CARS WERE DAMAGED. SUBARU OUTBACK COULD NOT BE DRIVEN. CAR WAS PARKED ON A VERY SLIGHT INCLINE. *TR