What's a pet to do, when the holiday house fills with sights and smells of the season and humans are looking the other way? Probably get into trouble, and pet owners should prepare to deal with toxic temptations, says an expert at the Cornell University College of Veterinary Medicine.

"This is a tough time of year for pets and their stomachs," said Larry J. Thompson, D.V.M., clinical toxicologist at the college's Veterinary Diagnostic Laboratory, where many pet-poison cases from New York and the Northeast are referred. "There are so many new and different things to check out, and cats aren't the only ones that are curious."

There's holly and mistletoe and poinsettia to pry from the mouths of pets, although poinsettia plants aren't as dangerous as some people think, Thompson notes. Tree decorations, tree preservatives and chocolate Santas can be problematic, as can all the batteries that power the gift gadgets. And that's just inside the house. Thompson offers this advice to help keep pets healthy:

• Mistletoe, especially mistletoe berries, can be very toxic to cats and dogs. Fortunately, most commercially available mistletoe substitutes plastic berries for the real thing. Holly leaves and berries can cause gastrointestinal irritation, vomiting and diarrhea; however, animals rarely swallow many leaves because the tough, pointed leaves are difficult to chew. Greens such as balsam and pine, while not strictly toxic, also can cause minor irritation for munching pets. The long-time fear of poinsettia plants can be traced to reports of a poinsettia variety that is native to Hawaii; most poinsettia varieties that are sold at holiday time are less toxic, Thompson said, and at worst will cause irritation of the mouth, excess salivation and perhaps vomiting. But some of the increasingly popular potted bulbs in the lily family can cause kidney failure in cats, he noted.
• "Tinsel on the tree is the big one," the Cornell veterinarian said. "Tinsel has no direct toxic effects, but it can cause gastrointestinal blockage that can be life-threatening. Cats seem to love tinsel." Styrofoam in ornaments or packaging presents the same threat of gastrointestinal blockage. And bubble lights contain methylene chloride, a moderately toxic solvent. "Chewing one bubble light is unlikely to cause much of a toxic problem," Thompson said, " but we worry more about the glass or plastic that the animal might ingest." Tree preservatives themselves are not particularly toxic, the poison expert said, but sugar-based preservatives may become hosts to bacterial growth over a period of time, and the bacteria may sicken a thirsty cat or dog.
• Cautions about chocolate and treat-hungry dogs refer to semisweet "bakers" chocolate, which contains much higher levels of caffeine and theobromine than does milk chocolate, the Cornell toxicologist observed. But too much milk chocolate -- with its high-fat content -- can lead to pancreatitis in pets.
• Dogs that chew on batteries risk acid burns in the mouth and physical damage from shards of metal. The smaller "button" batteries, although they are unlikely to be punctured, can lodge in a pet's esophagus. X-rays will reveal the whereabouts of batteries, which may have to be surgically removed.
• While small amounts of alcohol in drinks won't cause a problem for pets, somewhat more of the depressant will. Three ounces of liquor in a 10-15 pound animal can depress its nervous system and stop its breathing. "We recommend that people don't change a pet's diet at holiday time," Thompson said, "and that includes alcohol."
• A deadlier form of alcohol may lurk in the driveway or garage, where automotive antifreeze has been drained from radiators. As little as a tablespoon of ethylene glycol antifreeze can kill a cat, and a couple of ounces can kill a dog. The sugar-sweet taste of ethylene glycol is particularly tempting to dogs, according to Thompson, who advises pet owners to dispose of the material properly and see to it that neighbors do, too.
• And safety-minded parents who don't want Santa to slip on the ice may cause minor irritation for pets if they scatter rock salt, made of calcium chloride. Rock salt can cause irritation of animals' paws, or if they eat the salt, in their mouths and stomachs.

Pet first aid for rock salt ingestion is simple, Thompson said. "Give them a small meal, and maybe some water or maybe some milk, and everything should be fine."

Just be sure, he added, to save a glass of milk for Santa.