Final answer:
Old Major uses Parallel Structure, which is evident in the repetition and similar grammatical structure of each clause in his speech.
Step-by-step explanation:
The rhetorical device Old Major is using in this line from his speech: 'He does not give milk, he does not lay eggs, he is too weak to pull the plough, he cannot run fast enough to catch rabbits.' is Parallel Structure. Parallel structure involves using the same pattern of words to show that two or more ideas have the same level of importance, which is evident in the repetition and similar grammatical structure in each clause of the sentence.