I use to breed ferrets, so glad I happened to see this.
You know how kittens play when they are little, that little stalking jumping attack play? That's just them/nature - they are learning how to hunt. And even if you cat will never hunt, it loves the 'action play'. Ferrets are the same in that regard, only it last FOREVER.
And they LOVE the kind of play that includes jumping several feet into the air to swipe something from mid flight or off the wall or your shoulder, that is THE best part of the game for them. They knock the play thing to the floor and pounce on it.
I have yet to have one bird or squirl or mouse or anything else that enjoys this game. I've never had a ferret that is 'mean', but they spend their days looking for entertainment, play things and hiding things when that fails. (Hide everything leather and small or it will all end up behind large things you cant move - like refrigerator and stove and washing machine etc).
I had a bird that died after a play date with frank the ferret. Frank didn't hurt him at all, but it scared the bird so badly that he died several days later. The bird (who always had free range of the house accept for when I was sleeping or away from home), was so scared he wouldn't come out of his cage, wanted his cage door closed, would not eat or sleep or drink unless I was holding him. He just sat there with his eyes wide open until he died :(
So, no, I wouldn't get a ferret. AND, also, people think ferrets live in cages. No, That would be like making a cat or dog live in a pet carrier! They go in and out of cage as they please, usually just to use the litter box.