Certainly no such animal exists on Earth. So when someone quips, "If a frog had wings he wouldn't bump his butt," he is suggesting that some other person is being absurd. However, this whimsical question remains, what if frogs could grow wings? Could there be a flying amphibian of some sort somewhere?
This frog is a metaphor for Gnemo’s search for something extraordinary. It is the center of his need for adventure, and his drive for exploration.