Dog lovers have known for ages that pets get jealous. A new study has shown that this is true. The University of California conducted research into dogs and jealousy. A professor investigated canine jealousy after she saw her parents' three dogs behaving strangely. She said that when she stroked two of the dogs at the same time, they became aggressive towards each other. The two dogs tried to knock her hand away so they could get maximum attention. She said: "I was petting them….They wanted exclusive attention. That got me to thinking about jealousy in dogs."

The professor used a jealousy test usually used on children. Researchers conducted tests on 36 different dogs and recorded their reactions. The dogs' owner read a passage from a book while petting a toy dog with a wagging tail, and a Halloween lantern. Harris wanted to see if the dogs were jealous of the owner petting the toy dog and the lantern. She saw that the dogs were twice as jealous of the toy dog. A third of the dogs tried to get between the toy and its owner. The professor wants to understand jealousy more. It is a leading cause of non-accidental homicide.