Grain Co. purchases grain from farmers each fall to resell as seed grain to other farmers for spring planting. Because of problems presented by parasites which attack and eat seed grain that is stored for more than a few months, Grain Co., like all seed grain dealers, always treats the seed grain it purchases with an invisible mercury-based chemical to poison these parasites. Grain Co. sells the seed grain loose by the truckload to the farmers who will plant the seed. The Grain Co. trucks display signs that state: "Seed Grain. Not for Use in Food Products."

Farmer Jones bought a truckload of seed grain from Grain Co. She was present when the seed grain was delivered, and supervised the Grain Co. employees who unloaded the seed grain into her silos. She then used some of the seed grain to sow her field. When she found that she had some seed grain left over, she fed it to her dairy cattle. Farmer Jones sold the milk produced by her dairy cattle to Big Food Stores, Inc. ("Big Food"). Several of the people who bought their milk at Big Food became seriously ill, and the Centers for Disease Control (CDC), a government agency that investigates outbreaks of illness, determined that mercury poisoning was the cause of their illness. CDC traced the mercury to the milk that Farmer Jones sold to Big Food.

On what theory or theories might the injured milk consumers recover damages from, and what defenses should they anticipate, in actions against:

1. Grain Co.?
2. Farmer Jones?
3. Big Food?