i have noticed that one of my rats koala has a hunched back, when she walks it is hunched and so on. She is about 5 or 6 months old. She is a rescue and is still rather small. She has a cage mate that is her sister and her sister doesn't have a hunched back. She is eating and she doesn't seem sick. Is this normal for my dumbo rat to do or is there a problem? Please advise.