The sentence "The rat the cat the dog bit chased escaped" is difficult to parse because it is an example of a "garden path sentence." These types of sentences are structured in a way that initially leads the reader to interpret them incorrectly. The difficulty arises from the nested relative clauses and the lack of punctuation or conjunctions that would normally help clarify the relationships between the different parts of the sentence.

Here's a breakdown of the sentence:

1. The rat [that] the cat [that] the dog bit chased escaped.

   • "The rat" is the subject of the main clause.
   • "The cat [that] the dog bit" is a relative clause modifying "the rat."
   • "The dog bit" is a relative clause modifying "the cat."
   • "Chased" is the verb of the main clause, with "the rat" as its subject.
   • "Escaped" is the main verb of the sentence, indicating what "the rat" did.

The sentence can be rephrased for clarity as: "The rat that was chased by the cat that the dog bit escaped."

The complexity comes from the need to keep track of multiple layers of nested clauses, which is not typical in everyday language. This requires the reader to backtrack and re-evaluate the sentence structure, making it a challenge to parse correctly on the first read.