I Noticed Tonight I Had Some Sort Of String In

I noticed tonight I had some sort of string in my stool, i used an old tooth brush and wads of toilet paper to investigate, At first It looked like a stick or twig. Regular color poop, it was attached between 2 terds. with toilet paper and toothbrush, it was very hard to detach it. it had to be string. When it finally came apart it seemed to be like a grassy type but still string. I dont know what it could be, I do work around dogs alot too. What could this be a sign of?