I noticed something strange yesterday as I was bringing a balloon of Nitrous Oxide into the house. My dog appeared to be terrified of the balloon, almost like she knew something was up or "not right" about it.. she's never acted this way before. I would try to pet her and she would keep running away and acting strange while a staring wide-eyed at the balloon. Maybe the gas produces a certain frequency of sound in a balloon that dogs can detect? It was very strange.