One note of caution - pick a plant that is not toxic to cats. We use the grass they like to eat on their walks. It looks very much like our pots of cat grass, and in fact, one of our pots has gone crazy and the massive stalks have sprouted a wheat-type feather of seeds - very similar to the wild grown grass they munch.
And that brings me to another caution for the humans....while the head of seeds makes a delightful rattle, they WILL come off and spray everywhere in play! Not great for the house. Oh, and you'll need to judiciously play with such a weed dependant on where you live. The same things grow in Western Australia, but they are baked by the climate so the seeds are little daggers. We learned the hard way on our last holiday there with Kato - he got one of those seeds stuck in his throat. It did get swallowed, but had irritated his throat. The emergency vet said there are a lot of problems with these grass seeds, as they are so sharp, they can imped in mouths/throats or even in an animals skin. Fortunately over here in Victoria, the climate is much gentler, and the same grasses just don't do this. Moral of the story, use your judgement, and if in doubt, just rip off the seeds (like you probably did when you were a kid!).