Well, the cats have figured out how to open the sliding door.
We went to bed last night with all the doors closed nice and tight. We woke up, and the sliding door was open way wide and Jade was outside dancing through the tulips.
In the past, our cats have been able to open regular, hinged doors by either pulling or pushing them to open. But the sliding door is pretty heavy - it's got glass in it. I'm just waiting to find where they've hidden the crowbar - and the opposable thumbs to use it.