You might imagine that the most interesting thing we find in a pet’s stool sample is a parasite or two.
The truth is that we are occasionally surprised by an object hidden within the sample. Anything the nature of which is undetermined is classed as a UFO: Unidentified Fecal Object. Sometimes we have to rely on the (surprised/chagrined) pet owner for interpretation of the uncovered ingesta. Oftentimes, the object is easily recognizable.
Following is a sampling of items we have discovered during routine fecal examinations. I have added the pet’s breed, age, and weight, if known.

Baby wipe, ingested and passed by 3 mo. old Boxer pup, 13 lbs.

Ear plug, ingested and passed by 9.5 week old German Shepherd pup, 20 lbs.

Rubber ring, ingested and passed by 4 mo. old Maltese pup, 5.75 lbs.

Nail, ingested and passed by 3 mo. old Labrador pup, 15 lbs.

Elastic string, ingested and passed by adult cat, age and weight unknown.
The pets that passed the items above are alive and well, with no surgery required. Other pets are not so lucky.
As veterinary professionals, it is not difficult for us to imagine any of those objects becoming embedded or entwined in a pet’s stomach or intestines, provided it passes through the esophagus to begin with. Cats, in particular, are susceptible to swallowing string, which can strangle the intestines.
A pet that has swallowed an object it cannot pass may exhibit vomiting, diarrhea, loss of appetite, and weight loss. If you suspect your pet has eaten a non-food object, take him to your local veterinary emergency hospital immediately. X-rays and surgery may be necessary to remove the item.
Particularly when introducing a new puppy or kitten* to your home, pet-proof the house to remove tempting objects from their reach. Remember: Not everything eaten is actually food.
*Even adult pets are known to swallow non-food items.