Those sacks are excellent, make sure you dot throw them away when they go green ashtats when they are best 
I had this conversation with my mum this morning. I said Alice's is still clean after 6 weeks or so and she ignores it most of the time. When she comes down to the basement, she goes mad for the one that Kylie and Clapton share and adds her own drool
We went through the "Shelley has loads of catnip toys she ignores them" and me saying "She WILL play with the sack!"
+ they can be left lying around and no danger
(to the cats anyway
)
Lovely kitties btw
