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They're are different kinds of frogs. I live in a very rural area in southern Illinois and if you're sitting outside at night during summer the prevailing theme sounds very much like "ribbit". So I get it. Although obviously that's not exactly what noise they make it all of them. onomatopoeia animal noise/sound words are all exactly like this, limited and not exact so it's really not surprising at all. Even different human cultures use different ones.
