This movie is often praised for following the book in not avoiding the bodily functions and urges that are inherent to dog-ness. I'd say the movie doesn't just "not avoid" them, it wallows in them - to the detriment of the more meaningful and insightful story.
Such an earnestly honest and funny movie. I learned much about dogs (having never owned one) and a little about humans. And animation was the right medium for the matter-of-fact narrative: using live action would've bent the various scenes of dog behavior and anatomy towards gross and even obscene.