1.) Tinsel, ribbons, and ornaments: Although these decorations are not toxic, they can definitely cause problems with your pets. In particular, longer, thin decorations can cause major problems as they tend to turn into linear foreign bodies. Unlike a ball, corn cob, etc that may be eaten and removed fairly easily, longer string like objects tend to get hooked higher up in the stomach and intestine and then continue to move down the intestinal tract. This leads to a large amount of damage that tends to make it more difficult to remove and heal from.
2.) Holiday lights and candles: The constant flickering of lights or bright colors can be very attractive to pets. The problem with this is the electricity running through the lights. You may not get the reaction like in "National Lampoon's Christmas Vacation," but biting into a cord can cause significant mouth burns and possibly death. Make sure lights are out of the way of your pet.
5.) Holiday plants: The good news is that most plants will only produce mild gastrointestinal upset if your pet is exposed to them. Poinsettias, holly, and mistletoe typically fall under this category, but with large exposures there can be other problems, so always contact your veterinarian.
The best way to avoid a problem with your pet this holiday season is to keep anything that could be a hazard out of their reach. Have a safe and happy holiday season.