In a manner accessible to non-lawyers the study shows animals as a subject of the contract of sale in the light of the Polish civil law. This knowledge appears to be useful for a veterinary surgeon during the sale of animals in terms of the clinical examination both in determining their condition and health as well as their defects. The paper interprets the dependency of diagnosed defects in the perspective of a contract of sale. The article presents basic knowledge in the range of a veterinarian as a clinician and expert. It presents the knowledge about the physical and legal defects of animals based on the norms of the civil code and other Polish normative acts.