Now the crown of my cock was doing the job of thinking and not my head . It knew only one thing and that was blowjob and nothing else.

So I withdrew my cock out till only the head was in my Sis's mouth and again pushed it in with a jerk. I went all the way in and touched her throat. That was inconvenient for her so she put her one hand on the base of my cock and took it in her fist, so that more than that point it could not move in her mouth. Perhaps she was drawing a limit for my lundforsucking , till a point it was easy and enjoyable for her.