According to class materials prepared by Colorado State University, a common cause of true projectile vomiting is the blockage of the exit from the stomach into the intestines. The most common cause for such a blockage is the ingestion of a large foreign object. The Mayo Clinic warns that rarely, in infants, a serious condition known as pyloric stenosis can also be a cause.
The class materials prepared by Colorado State University state that there are generally several warning signs before vomiting occurs. The first is the sensation of nausea. This is followed by retching, spasmotic movements of the respiratory muscles with the airway blocked off by the glottis, which feels like vomiting without any actual production of vomit. Finally vomition occurs, where the airway is blocked off, and a combination of a downward push from the diaphragm and contractions of the abdominal muscles force the contents of the stomach out through the esophagus. Projectile vomiting is remarkable for both its forcefulness and the fact that, generally, these prior warning signs are absent, making it sudden and even surprising when it occurs.
According to the Mayo Clinic, pyloric stenosis is a malformation of the opening to the intestines found in infants, where the walls of the opening grow so thick that the passage is blocked. This condition must be corrected with surgery.