Catnip.

Few days ago I bought a "massage center" or what was the name of it, to girls. It has some kind of brushes on its side and in the middle is a "binkie". Under the binkie is a place for catnip. When I fill it with the catnip, goes Nelli crazy. Peppi doesn't really mind about it, she just stares Nelli because Nelli minds behest of them both: She bites the binkie, licks it and tries to make the massage center turn upside down, few times she has done it. When it turns upside down, Peppi eats the catnip from the floor and Nelli licks the floor so it's sticky. Funny how they react so differently for it. My other cat before these two, didn't react to catnip at all.