Animals

The most obvious example of animals in Magnolia is frogs. Characters also note that it's raining "cats and dogs."

While the second example might be seen as jokey foreshadowing, it's worth noting character family names that are also animal names: Jimmy Gator and Earl Partridge. This might be contrasted with the movie's numerous references to plants, most obviously the name of the film. It's interesting to note that the spouses of these powerful men have married names that combine the plant and animal kingdoms.