1. Rubber Bands and Hair Ties
A veterinary internist friend of mine examined a cat that the owner brought in because he had noticed a "hard lump" in the cat's abdomen. Turns out, the 11-month old Maine Coon cat had ingested many, many rubberbands over a period of months and they collected as a large mass in the stomach, requiring endoscopic removal.
Cats are sneaky too. I rarely see them chewing on these bands, but know that they are a hazard, even to seemingly uninterested cats.
2. String and Yarn
Unlike rubber bands and hair ties that tend to bunch up as a mass in the stomach, string can bunch up the intestines, which is quickly life-threatening.
The string, whether elastic or not, usually hangs up while the intestines keep moving (normal gut movemet called peristalsis). This creates an accordion-like bunching up, leading to tissue damage, ripping of intestines, and ultimately leakage of intestinal contents, causing infection and death.
String is another "irresistible" for cats, and once they start chewing it and swallowing, it is hard to stop (peristalsis in action). Be sure to pick up all ribbons, bows, and other string items to avoid a serious problem.
3. Food Items
Holiday gatherings are another risk factor for this, both in terms of food being out and "available" as well as guests sneaking pets one too many snacks. Be sure to keep snack plates and pets separate.
My Greyhound Purl, for reasons unknown to me, decided to chew open a pack of AA batteries. After a panicked count, I accounted for all of the batteries. A relief, as this type of problem takes a while to show up as a health issue, but it can be deadly. Even small watch batteries can be a problem.
Learn about:Battery Types and Toxicities
Always make sure medications (including vitamins and supplements) are out of reach from pets and children. Never give human medications to pets unless under direction from your veterinarian.
The gum itself isn't the problem, it is the sugarless sweetener, xylitol. The amount contained in different brands of gum varies, and each animal's sensitivity to this ingredient varies, too. Xylitol is also found in "sugarless" backed goods and candies.
7. Gorilla Glue
If enough of this glue is eaten (and it doesn't have to be much; it expands in the stomach), surgery is often necessary to remove the hard glue mass.
8. Packing Peanuts
Not worth the risk of intestinal upset or blockage. Keep these (annoying, in my opinion) packing materials out of pet's reach.