Cat intelligence
The brain of the domesticated cat is about long, and weighs . If a typical cat is taken to be long with a weight of , then the brain would be at 0.91% of its total body mass, compared to 2.33% of total body mass in the average human. Within the encephalization quotient proposed by Jerison in 1973, values above 1 are classified big brained, while values lower than 1 are small brained. The domestic cat is attributed a value of between 1–1.71 relative to human value that is 7.44–7.8. The largest brains in the Felidae family are those of the tigers in Java and Bali, of which the largest relative brain size within the "panthera" is the "tigris". It is debated whether there exists a causal relationship between brain size and intelligence in vertebrates. Correlations have been shown between these factors in a number of experiments. However, correlation does not imply causation. Most experiments involving the relevance of brain size to intelligence hinge on the assumption that complex behavior requires a complex (and therefore intelligent) brain; however, this connection has not been consistently demonstrated.
Common opossum
The common opossum is similar in size to a house cat. The fur of the opossum is actually yellow in the under-fur, but is hidden by the longer black guard-hairs that cover it, while the tail, fingers, and face are lighter "with the tail being without fur, somewhat similar to a giant rat tail." It can measure nearly 20 inches long. It has large ears that are usually black, and its face is usually a pale peach in color, with black whiskers and eyes that reflect reddish in light. With a body length of nearly a foot, and a tail that can reach almost two feet, the common opossum is one of the larger members of its family. An adult can weigh more than three pounds.