Food is eaten normally and passes to the back of the throat (the pharynx). The cranial oesophageal sphincter won't open and the animal retches the food back out of the mouth. This is a dangerous situation because some of the food can accidentally enter the windpipe and pass down into the lungs where is causes pneumonia. As the food is ejected most passes through the mouth, but some can also pass up the nasopharynx and out through the nose.
Last updated : October 2013