When choosing a Halloween costume for your dog, consider the following: Make sure the dog's field of vision is not obstructed. Choose a costume that is appropriate for your dog's size. Avoid costumes with small pieces that can be swallowed. Never leave your dog unattended in a costume. Consider a hat or bandana for dog's who have never worn a costume. Watch for behavioral signs that your dog may be stressed, overheated, or uncomfortable - if he's not happy, take the costume off.