Believe it or not, this is a proper English sentence:
Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.
In fact any occurrences greater than zero is a proper sentence. If you are into geek notation this is what it means:
Buffalo [buffalo...].
To find out what the sentence really means you can check out the Wikipedia page, Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo, where they can explain it a lot better than I can.
Also because the English language is so random, people think they can do whatever they want with it to make it proper, see this blog that documents unnecessary quotation marks.
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