My 7yr Old Went To The Bathroom And There Is

My 7yr old went to the bathroom and there is dark stringy fibers in greenish small pieces of stool. We have eaten avocado two days straight with dinner and he had a banana today with breakfast this morning . It is making me nervous because some medical websites say it's unchewed banana fiber and the picture looks almost exactly like it and then other pictures say parasite. I do have a picture that when you expand it shows it pretty well but have no way to know unless we bring him to E.R./Pediatric Dr. We just didn't want to rush out for something that is common or minor , maybe nothing at all. Any input ?