Animals do not emit sounds for the sake of emitting sounds, they do so with specific intentions, desires, and goals, and as a result of specific systems that have developed towards the end of a complex system of communication involving vocal and auditory mechanisms, sound waves, and cognitive elements giving the capacity to process and generate these patterns of sound.
It's funny to me because I know that some people would look at this application and think of it as a hilarious joke: "Understand animal sounds? Ha Ha Ha good one Google! As if! Chinese Room! Hurf Durf! IMPOSSIBLE!"
It's also funny to me because I know that some hackers will look at this and be inspired to spend their spare cycles researching and developing this application, and wind up making a small fortune when they put it on the app store.
It's also funny to me because I suspect that some crafty googlers have already done this and are using the video and google's reputation for funny April Fools Day Jokes as a viral marketing tactic for their April Fool's Day Day-After joke, where they release the fully functional application, having developed it during their allocated "pet project" time.
Good one Google!