"Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo." is a grammatically correct sentence used as an example of how homonyms and homophones can be used to create complicated constructs

"James while John had had had had had had had had had had had a better effect on the teacher" is an English sentence used to demonstrate lexical ambiguity and the necessity of punctuation,[1] which serves as a substitute for the intonation,[2] stress and pauses found in human speech.[