The following sentence is grammatically correct: Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.

The word ”buffalo” in the sentence has three meanings: the animal, the
city in New York and the act of ”buffaloing” which is another word
for teasing or bullying. Here is another way of looking at the sentence:
THE buffalo FROM Buffalo WHO ARE buffaloed BY buffalo FROM Buffalo ALSO
buffalo THE buffalo FROM Buffalo.”

Another grammatical puzzle is ”James while John had had had had had had had had had had had a better effect on the teacher.”