wikipedia

"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 speech.[3] In human information processing research, the sentence has been used to show how readers depend on punctuation to give sentences meaning, especially in the context of scanning across lines of text.[4] The sentence is sometimes presented as a puzzle, where the solver must add the punctuation.