11. Sam went to E-Z Shop to pick up some groceries. Sam was in a bit of a hurry, and began walking swiftly down the aisles of the store. Sam forgot about a nagging knee injury that often reemerged when he moved too quickly. Sure enough, as Sam was briskly walking down aisle 9, where a store employee had neglected to clean up a spill, Sam's trick knee went out and he fell to the floor, just before he reached the spill. If E-Z Shop avoids liability in this case, it will probably be because