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 ?