The book, it's interesting. The chair, it's comfortable. The cake, it's tasty. The girl, she smiles. The boy, he sighs. The person, they giggle. The cat, she yawns. The horse, he breathes. The pig, they snore. Animals are not things and so we avoid referring to an animal as "it". That language reinforces the idea that they are objects, not the living, feeling beings that they are. He, she, they, which pronoun is not really important if you don't know their sex, what matters is that we refer to them as beings, not things. Worried about grammar? Don't be. Grammar changes and there are many things in life more important than grammar. 😉✌️