A balloon bobs across the room and your dog backs away. It may look harmless to you, but it moves in unpredictable ways and can make a sudden loud sound. Let your dog leave. Do not hold them close to it or push it toward them for a sniff. Put the balloon away, and keep uninflated pieces and popped fragments out of reach, swallowing them can be dangerous.
If the dog is frightened by many ordinary objects or the reaction is new and intense, discuss it with your veterinarian. A qualified, reward-based behavior professional can help if fear is spreading or affecting everyday life.
Make the object less surprising
If balloons will be present in your home, begin with a deflated balloon out of your dog's reach and a comfortable distance from their resting place. Reward a relaxed glance and put it away. Later, introduce a still, secured inflated balloon at a distance where your dog remains comfortable. Do not let it roll into the dog or pop near them. Keep each practice short and give them a clear exit. If they refuse food, tremble, or hide, the exercise is too hard.
You may decide that your dog simply stays in another room during a party. That is a sensible plan, not a training failure. There is no need for every dog to like balloons, only for them to be safe and able to relax. If pops and other sudden sounds are the concern, the sudden-noise fear guide may help you plan quiet-day practice, keep balloons out of reach now
Sources: Dogs Trust: What to do if your dog is scared of loud noises. Cornell University College of Veterinary Medicine: Gastrointestinal foreign body obstruction in dogs.