How do you cast a dog in a movie?

Ken Marino’s newest movie Dog Days tells an interconnected story of the people of Los Angeles and their dogs, as they uncover life lessons and form new relationships—it’s basically Love, Actually with dogs. Obviously there are a ton of canines in the movie, which begs the question: How did they cast dogs in the movie? In the video above, Marino tells about the casting process, which is actually not that different from that for humans.