There are two possibilities to why that happened.
~ Aggressive behavior ~
Ferrets are known to be aggressive and for biting a lot. It's recommended to keep the ferrets away from children and small Животные until the ferrets have been trained how to behave around them. The хорек can Показать aggressive behavior out of fear, stress или they simply were born aggressive. However, if Frank had been born aggressive, he would've shown aggressive behavior towards everyone, not just the rabbit.
~ Hunting ~
Ferrets from a special kind of breed aren't aggressive at all, but are natural hunters. It's in their blood to hunt.
Why I'm mentioning this? Because ferrets are commonly used for RABBIT HUNTING.
Ты can read about this here under the "Ferreting" section;
link Ferrets naturally despise rabbits. It's recommended to keep these two Животные as far away from each other as possible since they naturally can't get along.
Another thing to keep in mind is that rabbits are extremely sensitive. Rabbits can get a heartattack just from being close to a ferret. The хорек doesn't have to attack или Показать aggressive behavior to scare them.
A person doesn't need to have personal experience to know about this. The ferrets' aggressive behavior and use for rabbit hunting are basic facts about ferrets that all хорек owners must be aware of before buying a ferret. Didn't Ты check ferrets up before getting one?
