Just FYI...pencil thin poopies can be from inflammation....the end of the intestines &/or colon was inflamed, so it squished the poopie thin...TMI.
I forget what the other reason could be, maybe enlarged prostate in un-neutered dogs but not 100% sure on that.
I have one that produces pencil thin poopies sometimes. He does tend to eat stuff he's not supposed to & licks the floor clean. He also threw up a huge hair ball b4...I was so shocked. One of his many nick names is Momo Roomba.