1. What are baby hiccups? Hiccups in babies are a reflex phenomenon caused by gas from the stomach moving upward in the esophagus. This phenomenon usually causes the baby to make a \”gurgling, gurgling\” sound, and sometimes causes slight discomfort. 2. Why do babies hiccup? 1. Swallowing too much air. When your baby is breastfeeding or taking solid food, if the rhythm of sucking and swallowing is not correctly grasped, it is easy for too much air to be sucked into the stomach, causing hiccups. 2. Indigestion. If breast milk or formula milk contains too much lactose or protein, it may cause indigestion in the baby.