Tinkle Tells You Why

Why do we sneeze when we put something like a string, in our nose?

As you no we breathe air in through or nostrils. In the nose we have hair and mucus to trap any particle which may be present in the air. Sneezing is a reflex action is to dislodge any substance from the nose. When you irritate your nose with a piece of string, a strong exhalation of the air in the form of a sneeze occurs to throwout whatever it is irritating the membrane of the nose.