While many dogs like to mouth a favorite toy, they may not have a fixation stronger than a teething toddler with a favorite pacifier, like my golden retriever Shakira does with a tennis ball. Why does four-year-old Shakira greet us with a tennis ball in her mouth, and grab a toy to take with her in the morning when she leaves her kennel to do her business?

"It is because retrievers are bred to retrieve game and hold it gently with a "soft mouth" so as not to crush it," explains Dr. Nicholas Dodman, a veterinary behaviorist at the Cummings School of Veterinary Medicine at Tufts University and the author of "Dogs Behaving Badly." "The offering is also powerfully reinforced by owners who are thrilled by their dog's nifty behavior."

According to Dr. Rolan Tripp, founder of www.AnimalBehavior.Net, "most dogs can learn to bring a toy to their owners at homecoming but retriever breeds excel at this activity."

"Natural behaviors — such as a retriever hunting dog wanting to bring back a downed duck to its master — are often redirected in house pets. In this case, the retriever brings back a dead tennis ball to its owner," says Gary Landsberg DVM, DACVB (veterinary behaviorist), of Doncaster Animal Clinic in Ontario, Canada, and author of the "Handbook of Behavior Problems of the Dog and Cat" (2nd edition). "Anecdotally, I see and hear about this far more commonly in golden retrievers and to a lesser extent in Labs.

"This is also seen in the wild canids," reports famed biologist Dr. Marc Bekoff, professor of animal behavior at the University of Colorado-Boulder and author of "Animal Passions and Beastly Virtues: Reflections On Redecorating Nature."

"I've seen wild coyotes carry things in their mouths like an offering, especially pups when an adult returns to their pack."

Similarly, a human mother may present an infant to the father returning home after a day at work. See what you've missed all day?