i have an encouraging anecdote.
a very close family friend’s kid behaved like that from about the age of 3.
after an incident at school he got a diagnosis of ASD and ODD, there may be other diagnosis that I am not aware of.
he just did what he needed to in order to get what he wanted. He would do that to a gerbil because he’d see it like a fidget spinner and not a creature that could feel pain.
About 6 years he shoved my toddler out of his way, really booted her and she had a badly grazed face from the pavement. He didn’t care, the baby was in his way so he felt that he simply solved a problem.
by the end of primary school he was a problem because he was getting stronger and the angry behaviour was escalating - the other kids would purposefully wind him up in order to laugh at him and so he’d hurt someone and then he was in even more trouble.
He was not a boy who needed friendships but he knew that he was not liked and that bothered him. It was all very complex and hard for his family. He was a smart, funny boy who had a total lack of insight into other people.
he landed up on some anger management programme at CAMHS which included the family and school which was a long term thing and worked Well. He is now about to start Uni and is doing really great.
He is exceptionally bright and understands how people tick on an intellectual level. he is still not got friends but he has the ability to manage relationships wirh his Saturday job colleagues- mainly because he knows that he wants the money from the job so he has to get on with them. It is enough and the thing is that he is genuinely happy.
his mum says the thing she is glad about was early diagnosis - that’s what got them into this CAMHS problem.
good luck, it sounds really hard. I hope your gerbil is ok. Maybe get a vet check incase it needs pain or infection managed? Pray animals will hide pain.