A movie about what pets do during the day is a winning premise. Of course we want to know what those adorable creatures with whom we share our lives are up to, and so “The Secret Life of Pets” is here to explore those possibilities. Turns out their days are much more dramatic and crazier than ours, with all sorts of underworld pet societies and warring animal factions. There’s apparently a lot to keep secret in the lives of these pets.