Max heard a tinkle as one of "Dog" vial slipped off the coffee table and fell to the floor. He walked into the living room, and saw the strange vial rolling across the floor. He picked up the empty vial, and examined it. Max couldn't read English, but he did recognize the picture of a dog on its label. He spied the "Human" vial lying on the carpet next to where he drank from the puddle. He examined the vial in his hand, and recognized the picture of a "Human" on the label.
It didn't take Max long to figure out what happened. He had drunk from the one marked "Human" and changed, while the girl must have drunk from the one with a picture of a dog and changed into one. He began to look through the box on the table. There seemed to be a endless collection of vials, each marked with a different animal. He saw one that appeared to be duplicate "Human" vial. It had a picture of a human female, and a strange symbol of a circle with a cross poking out below it. He recognized the symbol. He had seen it in the kennel, above the cages of some of the bitches. Suddenly, he understood what it meant and he got an idea.
He walked to the mirror and examined himself again. He really did look like a male version of the girl. If he had the right equipment, he was sure he could pass for her. Then he could escape his terrible life.
Max hated being a pet, being forced by John to complete seemingly meaningless tasks for scraps of food. He hated being subservient to the humans. But now was his chance to become one, to become a master instead of a servant. If the girl wanted to be a dog, that was fine with him. It would require a sacrifice, though. Max looked at his genitals and winced. He would miss being a male. But it was worth it if he could escape. He quickly downed the entire contents of the female vial and waited.