He, she, it: Pronomes usados para animais em inglês

Hello friends!

I'm reading the book three of the Harry Potter's serie (The Prisioner of Azkaban) and come across a part of the book where they (Hermione and Ron)
Talk about Hermione's cat, Crookshanks. I'm really in doubt of how talk about animals in English 'cause sometimes they use "it" and sometimes they use "he/his" to refer to the pet. Here's a small part of the conversation about this issue:

Hermione opened her mouth to argue, but at that moment
Crookshanks leapt lightly onto her lap. A large, dead spider was
Dangling from his mouth.
“Does he have to eat that in front of us?” said Ron, scowling.

Sometimes in the book (and in other books i've read) they refer to the cat with "it" but sometimes with "he/him". Can I use both? Thanks in advance.
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