“That that is is that that is not is not is that it it is” – add punctuation, and this sentence transforms from babble to sense. But, depending on which punctuation you add, it can make four different sentences.
Syntactic ambiguity is a lovely thing. Here are the examples of how punctuation transforms this sentence, from Wikipedia:
That that is, is. That that is not, is not. Is that it? It is.
That that is, is that that is. Not is not. Is that it? It is.
That that is, is that that is not. Is not “is that“ it? It is.
That that is, is that that is not, “is not.” Is that it? It is.
Shakespeare could communicate multiple meanings with a single sentence, as you can see from this quote from Henry VI:
The duke yet lives that Henry shall depose.
You could reasonably read this as “Henry shall depose the duke (who lives)” or “The duke (who lives) shall depose Henry.” A more modern example is from the song Lola:
I’m glad I’m a man, and so is Lola.