Holden mimics Old Spencer's mania for nodding his head when listening to someone and mimics the relaxed communication Old Spencer talks to him with.
We can arrive at this answer because:
Holden imitates the relaxed tone that Old Spencer speaks, in addition to imitating Spencer's mania for shaking his head when someone is talking.
This question is about "Catcher in the rye" and you can find more information here:
https://brainly.com/question/3460870