All forms of chocolate, especially baking or dark chocolate can be dangerous, even lethal, for dogs and cats. Symptoms of chocolate poisoning may include vomiting, diarrhea, rapid breathing, increased heart rate, and seizures. Halloween chocolate containing the artificial sweetener xylitol can also be poisonous to dogs. Even small amounts of xylitol can cause a sudden drop in blood sugar and subsequent loss of coordination and seizures, while xylitol toxicity in cats has yet to be established, it's better to be safe than sorry.
Pranksters have been known to tease, injure, steal, and even kill pets on Halloween night so try and keep all pets indoors on halloween night and on the nights running up to halloween.
With the constant stream of callers for trick or treats there will be a lot of door opening and loads of children/parents dressed in costumes which can scare and make your pets nervious, try and keep them away from the constant noise and give them a quiet space away from the front door to relax in.
Although they are relatively nontoxic, plants such as pumpkins can induce gastrointestinal upset should your pets ingest them in large quantities. Intestinal blockage can even occur if large decorations are swallowed.
Should they get too close, they run the risk of burning themselves or knocking it over and causing a fire.