I had introduced placing a wet piece of tissue on my grandkids foreheads whenever they had hiccups which they have used on occasion and strange enough it seems to work.
Just recently my niece started with hiccups and she remembered so she went to her grandma and asked to have it done..voila..gone. I did look it up a while back and it was said to do the trick 85% of the time but there is no explanation on how it works.