Ours love tennis balls. However, I have to quickly retire them after a week or two. Why? The white part that goes around it, is some sort of rubberish material. As they chew, they're not trying to get at that, but it comes up after chewing the fuzz. Unfortunately, it loves to crack, and so I pull off as much as I can, but when they're chewing, you'll find that some just falls off. It's extremely easy to eat parts of it if you're a ferret, even if you're not trying to. That's my warning on tennis balls (especially the mini-ones you see in the pet stores). My other warning is the tops of kongs - even the black, tough ones. I wish KONG would redesign it so that it didn't have that nub at the top. It's honestly pointless and it's the only part that makes the toy dangerous, over time, to ferrets. It will begin to crack and split into numerous small pieces if you have a real chewer. With new kongs, I just take kitchen scissors and cut the nub off clean. I do have to be careful because it's kind of hard to do without the nub flying somewhere where you can't find it. L [Posted in FML 6983]