Dogs are known as man's best friend. They have always been known for their loyalty, but every now and then, even the most loyal dog gets bitten by the green-eyed monster.

Canine jealousy is something psychologist Christine Harris put to the test. Her recent study, "Jealousy in Dogs," demonstrated that it is possible for dogs to show signs of jealousy, indicating that jealousy is more primordial than recently believed. She joins Take Two to talk more about it.