A cattle rancher bought cattle from a neighbor who, both verbally, and in their contract, assured the cattle rancher that the cattle were "disease free." Unfortunately, one of the cattle died from a disease, and the disease spread to other cattle in the herd, causing them to lose weight, and thus value for sale. The rancher seeks to recover the losses ($750 in veterinarian bells, and approximately $17,000 in decreased sale weight) from his neighbor. On what theory(ies) can he do so?