CHICAGO (CBS) — Halloween is a busy day for veterinarians, as candy is the most common hazard for pets.

Chocolate is toxic for dogs, and for those pets trying to sneak a snack, candy wrappers can cause vomiting or potentially block a pet’s digestive system.

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Dr. David Gonsky, who is the founder and chief medical officer at West Loop Veterinary Care, says it’s best to keep your pet inside during the Trick-or-Treat time of the holiday.

“Some people love to play pranks and unfortunately some of our cats, especially black cats, are really at risk during Halloween,” Dr. Gonsky said. “If you have those kinds of pets, keep them inside — it’s just safest for them.”

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According to the Anti-Cruelty Society, wires and plugs from electrical lights can also post a threat to pets. “Electrical shock from chewing on cords or injury from plastic or glass bulbs is possible,” the organization’s website says. “Make sure they are kept out of your pet’s reach.”

Dr. Gonsky added that costumes with masks could also cause anxiety for dogs and cats because they can’t read facial clues.

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If you think your pet may have ingested something harmful, the Anti-Cruelty Society recommends calling your vet or going to your nearest animal hospital immediately.