Zimba was on a leash while we tried to find out how he escaped from our veranda. The others never got out, only him. We figured it out after a while, and put a stop to it. It didn't feel safe for him to go out that way, from the first floor. At some point he figured out how to get back in too!
A home grown treat in a box! Probably not as tasty as regular outside grown grass though. And the mess... I don't think I'll ever give them this inside again, it is incredible how much mess a cat or two can make with a box like this in a single night!