Drink water continuously for 30 seconds, holding your breath as you do. This will resynchronize your swallowing mechanism, so you don't hiccup. I believe it is a result of your throat trying to clear itself of a foreign object such as an apple core piece. Even after the apple core piece is gone, if it goes down, your throat is still trying to resynch itself, and only by trying the method I just posted do you have a chance of clearing the hiccups. If this fails see a doctor. Also get completely rid of the apple core and or drink water with apples, pears, etc.