A hiccup was an involuntary movement which impaired speech, interrupting with such sounds as hic!. As Liz Shaw explained, this was "simply the diaphragm pulling down spasmodically rather than smoothly, usually through eating too quickly or nervous tension." As she elaborated, a hiccup most often resulted, quite simply, from stomach trouble or indigestion, when excess acid would be formed during the process of food digestion. Low fibre levels could also lead to this state.
Non-medical remedies Liz knew of included "surprises, drinking a glass of water upside down, a spoonful of something like sugar on the tongue", and holding one's breath while counting to 50. She also suggested a diet and digestive palliative, and further recommended running on the spot to work on regulating breath control.
In 1539, however, hiccups were believed to result from an imbalance of the humours. King Henry VIII was experiencing hiccups, so Liz set to work on fixing his problem, with her knowledge of 20th century chemistry and medicine. She cooked up a soothing alkaline for his upset stomach, a gentle sedative, and made a stink bomb that made a loud noise when it was set off, in order to scare him.
Her various attempts at relieving the King of his ailment failed, and she and the Third Doctor, who finally joined her, made an attempt to shock the King with the TARDIS' dimensional transcendentalism. They soon discovered, however, that the King had cataracts, and so was practically blind, accounting for why he was not easily frightened. Once the Doctor cured him of the cataracts with his sonic screwdriver, the King stepped inside the TARDIS for the third time, and the hiccups finally ended. (PROSE: Hiccup in Time)