Just after the muscles start to move, the glottis shuts off the windpipe to produce the characteristic "hic" sound.

BBC: Why we hiccup

This latest theory, originally published in the journal BioEssays and reported in New Scientist magazine, says the key to hiccuping lies in a group of animals for whom combining closure of the glottis and contraction of the "breathing in" muscles does serve a clear purpose.

BBC: Why we hiccup