Andrea was walking down the aisle in the local Slater Brothers supermarket. Moments earlier, a customer knocked a container holding a slippery liquid substance onto the floor, and it broke. Andrea, who was following right behind that customer, and through no fault of her own, slipped on the substance and broke her arm. Slater Brothers has a policy of having an employee walk the aisles of the store every ten minutes. Two minutes before the accident, a Slater Brothers employee had followed the schedule and walked the aisle where Andrea was hurt. Andrea sued the Slater Brothers for negligence