Real Chocolate Company (Real) makes a box of candy, which it sells to Sweet Things, Inc. (Sweet), a distributor. Sweet sells the box of candy to Tasty Candy Store (Tasty), where Jill buys it. Jill gives the candy to Ken, who breaks a tooth on a stone that was in the box and the same size and color as a piece of the candy. If Real, Sweet, and Tasty were not negligent, under what legal doctrine can they be held liable for Ken’s injury. Why or why not?