Why are dogs and cats the most popular pets?

I personally think that dogs and cats have more personality than other domesticated animals. They seem to have the ability to understand if we are sick or hurting. Especially dogs. They get excited when we are gone and come home. They are cuddly. Some dogs make wonderful exercise partners. I know I would never leave the house for a walk in the WI winters if I didn't have my dog begging me to take him. There's nothing like a warm dog or cat curled up on my lap in the winter when I'm cold.