I'm with Mmario and GUESTmg: Sugar.

My grandmother's remedy (70 years ago) was a teaspoonful of sugar with a little peppermint extract. In the mouth, and don't swallow, but let it dissolve by itself.

In later years I found (because I didn't have the peppermint extract available) that a spoonful of sugar under the tongue, held there without any attempt to "chew" it or swallow it, letting it dissolve, works wonders.

There's also breathing in and out in a paper sack. That one makes physiological sense. A higher carbon dioxide level slows the breathing cycle,and evidently upsets the hiccup cycle. Easier and more effective than trying to do it by holding your breath.

Dave Oesterreich