From a scientific perspective, omnivores pose a contradiction for the classification of animals. Explain.

 By definition, omnivores are animals that can process and derive energy from plant and animal matter. However, some animals, which are classified as herbivores, are known to consume animal products. Cattle, for instance, reportedly gnaw on dry bones for particular minerals. Similarly, carnivores such as cats are known to consume plant matter occasionally. This helps them regurgitate indigestible matter such as hair or bones. They may also consume plant matter for its laxative properties. Hence, the definition of omnivores arises certain contradictions among the scientific community.