Since the spell has a range of Personal, you are the target of the spell rather than the animal. Thus while anyone can observe the noises and gestures the animal is making, only you gain the benefit of understanding the answers the animal is giving. They are the same noises and gestures the animal always makes. Anyone who observes you asking the questions sees you barking like a dog or mewing like a cat or whatever, but because of the spell, you're making the particular barking or mewing that conveys the question you want to convey.