Clinical signs seen vary with the type of material and where it is lodged. Some animals may regurgitate up the offending material right in front of the owners or veterinarian. An object in the intestines leads to anorexia, vomiting and very little stool produced since digestive processes have come to a halt. In severe cases the animal runs a fever and becomes lethargic due to ileus. Sometimes the string cuts through the intestinal tract producing signs suggestive of peritonitis; characteristic radiograph "ground glass" appearance and extreme abdominal pain.
Cats are fascinating creatures but have an affinity and absolute attraction to linear foreign bodies. I have always asked clients if they sew or knit sweaters! If so, I have asked them to make sure the cat is kept out of the room to prevent not only yarn or thread from being swallowed but also preventing needles from being snarfed down by the creature.
Sometimes, the diagnosis is obvious. Such was the case when a small dog was presented with a balloon hanging out of its mouth by its string. That day, the owners held a birthday party for their young child. Surgery had to be done on that case. Cats are different from dogs. I made it a point in all vomiting cats to look at the base of the tongue (frenulum). If you are lucky, you may find string wrapped around there if the patient is cooperative. In most cases the string is already lodged in the intestines. The string is cut at the tongue base and removed through a gastrotomy or enterotomy.