This is called center embedding, and it's actually the subject of quite a lot of research. Some of this research has led to a distinction between grammatical (w

This is called center embedding, and it's actually the subject of quite a lot of research. Some of this research has led to a distinction between grammatical (which a sentence like "The cat the rat the dog bit chased escaped" may be) and acceptable (which such a sentence is not). Other research has deemed it agrammatical and unacceptable. Here's a helpful presentation summarizing some of this research: https://depts.washington.edu/lingconf/slides/Bader&Haeussler.pdf https://depts.washington.edu/lingconf/slides/Bader&Haeussler... The sentence the comment the user replied to included parsed with difficulty.