Sometimes a sneeze is a solitary 'Achoo!' Other times, sneezes come in twos or threes, leaving those in earshot wondering exactly when to sneak in a 'bless you.'
These multiple sneezes may be seem excessive, but they're actually helping people clear irritants out of their airways. Typically, you sneeze because you end up with foreign particles in your nose. The sneeze is the way to get it out.