After reading yours and Vorpal's comments, some things now become clear to me ... after nearly 9 months. When I had my interview, the IO first started talking about how big my file was, and maybe I was an asylum case, but then he realized that it was employment throughout. I just acknowledged and moved on. This was on the way to his office. After the oath, he started going through the file and started complaining about how his shoulder was hurting and he did not want to come to office that day. I again mumbled (not really) something courteous and waited for the questioning. Then he started off on how a surgery will help his shoulder ... this is when I "got" that he wanted to talk ... and wanted me to talk ... not sure what was the trigger, there may have been something else too [ maybe the english test happened this time ].
On my side, I was not expecting a hostile interview, but at least an interview and this kept me from talking much from my side. But seeing his signals were that he wanted to talk, I eventually changed tack and engaged in a conversation ... maybe 5-7 minutes. At the end of it, he went through the N400 almost at a super sonic speed, and gave the "recommended for approval" letter.
I thought it was weird then, but realized even then that I was expected to talk. Now, as they say - I know the rest of the story...
[ BTW, after the approval, I commended the IO pointing to the file ... saying that however clean one's file might be, we are always anxious when we walk into such an interview, and I wanted to thank him for not letting me feel like an interview. He said that he was glad to hear that, and also that apart from the day of the oath, this is likely to be one day we remember for the rest of our life, and as long as he is satisfied to the genuineness of the case, he sees no reason to give us a hard time and in fact wants to work to make it memorable. I never posted it here because I joined this board after my interview ... when trying to figure out the oath date ... but Bob's and Vorpal's comments somehow reminded me of this. ]