The next time you sneeze notice how you take a sharp intake of air. This air is then forced out of your nose at the same speed as wind in a hurricane!!! This is more than enough speed to expel your mucus/snot from your nose. As your body tries to clear the irritant or infection.
Great question. Lots of things happen when we sneeze:
1) Your intercostal muscles (the ones between your ribs) and diaphragm contract, increasing the volume of the chest and pulling air into your lungs – just like when you take a deep breathe in.
2) This air gets trapped in your lungs.
3) Your stomach and chest muscles then contract, increasing the air pressure in your lungs.
4) Your vocal chords then relax, forcing the compressed air out of your lungs in the form of a sneeze.