My dad's outdoor cat is slowly becoming an indoor kitty. Over the last few months we've been letting him in for longer and longer periods of time, sometimes overnight. One day last week he was inside all evening, and then my dad put him out. Come morning, my mom opened the sliding glass door, and he zipped in off of the porch. Apparantly at some point during the night he had managed to work the screen door open and get onto the porch. Last night I caught him trying to use his weight to slowly push the sliding glass door open, when he wanted out. He is by far the most intelligent and articulated cat I've ever seen, between his prehensile tail and damn near opposable thumbs.