short pencil thin poop

I had skinny pencil poops when I had a stricture in the colon (colon is gone now). This is something to tell your doctor because it might need to be scoped again.
My case was unusual: strictures usually happen with crohns, not UC (I have UC) so that with UC the stricture usually means a malignancy but in my case it didn't. However, it was about to cause a shut-down and since my UC was getting worse and not responding to anything, we dedicded to have the colectomy in a planned way, instead of as an emergency situation.
Do speak with your doctor about this.

     I had skinny poops when suffering with ulcerative proctitis.  However, I certainly would have this checked out by either a colorectal surgeon or GI doctor.