The answer depends on the criteria for assessment.
When determining the smartest animals, scientists often use a "human measure," which can lead to subjective conclusions.
The title of the smartest animals is usually claimed by primates such as chimpanzees, gorillas, and orangutans. These animals sometimes use tools and can learn sign language. For example, the famous gorilla Koko knew over two thousand words.
Other animals also demonstrate impressive intelligence, including domestic dogs and cats, rats, crows, pigs, elephants, dolphins, and even octopuses.
