Here's why:
* Sudden expulsion of air: The force of the sneeze expels air rapidly from the nose and mouth, creating a sharp, explosive sound.
* Vocal cords: The vocal cords often vibrate during a sneeze, contributing to the "choo" sound.
* Nasal passages: The shape and size of the nasal passages can also influence the sound of a sneeze.
While "atchoo" is the most common sound, there are variations depending on individual physiology and the force of the sneeze. Some people might even sneeze with a "hak" or "he-he" sound.
Ultimately, the exact sound of a sneeze is subjective and can vary quite a bit!