Mucus in your stool. Very common. Can also be food related, the digestive process changes the color and appearance of most things you eat. This could be a fibrous remnant from a fruit or vegetable that did not dissolve as well, but it looks like a mucus string. Your intestines secrete mucus to aid in the movement of the bowels. Sometimes more mucus is produced when certain kinds of foods are processed and or if a there is allergy or infection that provokes an immune response. Just like the immune system triggers excess mucus production in the sinuses during an allergic reaction, sinus infection, or a plain old cold virus, similar responses occur in other mucus membranes around the body including any the intestines. Roundworms generally do not get that long either. You can Google images of "roundworms in stool" and see how small they actually are. The internet is both your friens and your worst enemy. So many online sources are not reliable so make sure you look at the source of the image because it might even be from another forum like this. You want to be sure you are looking at a picture that is published from a source that is informative, like educational, medical, reference (like an encyclopedia) or news related site. Otherwise you are getting information that is more than likely uneducated and subjective. Some images are even posted as a joke. Just be sure to look at it on the website that displays it by clicking the link under the image in the search page. You certainly don't want to scare yourself too much! I hope everything works out for you!