Almost every dog owner has experienced jealousy in their dogs. This is manifested by vocalizations, agitated behavior and pulling on a leash. What researchers have discovered is that a dog acts jealous when they imagine that their owners are interacting with a rival. What is important about this study is that when a dog acts jealous, it shows that the dog has self-awareness. The study also showed that dogs act in a similar manner as children who are jealous. Dogs are one of the few animals that have this human-like behavior.  

What further illustrated the intelligence of dogs is that the dogs in the experiment only reacted to a perceived social rival and not an inanimate object. This shows that they are capable of analyzing the situation.

It is exciting to learn more about the mind of a dog. It is too bad that similar experiments cannot be conducted on cats. I personally feel that cats are at least as smart as dogs.