A hiccup is an unintentional movement (spasm) of the diaphragm, the muscle at the base of the lungs. The spasm is followed by quick closing of the vocal cords. This closing of vocal chords produces a distinctive sound.
American Cancer Society website. Hiccups. www.cancer.org/treatment/treatments-and-side-effects/physical-side-effects/hiccups.html. Updated June 8, 2015. Accessed January 30, 2019.
Petroianu GA. Hiccups. In: Kellerman RD, Rakel DP, eds. Conn's Current Therapy 2019. Philadelphia, PA: Elsevier; 2019:28-30.
US Department of Health and Human Services website. Chronic hiccups. rarediseases.info.nih.gov/diseases/6657/chronic-hiccups. Updated December 1, 2018. Accessed January 30, 2019.