I'm sorry to have to correct you there, but as revolting and rare as it is, yes it is possible to vomit up actual faecal matter. There are medically documented cases. The majority are caused by intestinal impaction (due to solid faeces, tumours or scar tissue). A smaller number are caused by paralytic ileus (the bowel fails to move food along, more common in elderly people but can sometimes be the result of excessive opiate use). The most outrageous verified case involved an African man whose doctor botched a routine haemorrhoidectomy and sowed up the entire anus.
The word is copremesis or faecal vomiting, and means exactly what it says.
It' s more common for the bowel to eventually rupture, resulting in life-threatening contamination of the abdominal cavity, or for parts of an impacted bowel to die, again leading to sepsis. But if a person keeps eating food which cannot be passed, it can indeed 'back up' to the point where excrement will be forced through the pyloric sphincter into the stomach.
PS my mother was a surgeon and has seen this happening (it was an elderly patient with untreated bowel cancer).
