Doors were put on earth to be opened. Rudy could open cabinet doors, didn't get in the cabinet, just opened them. He was bound and determined to get into the antique wardrobe doors, but hadn't quite figured them out. He would just bang on them, and that didn't work. If he would have lived longer, he would have figured out doorknobs. I saw him wrap his paws around them several times.
The most interesting time with him and door knobs was when my parents stayed with us. We were dog sitting, and the dogs sleep with Art. Mom and Dad had the spare room, and I had the couch. I was reading, and I heard a terrible rattling upstairs. And then it happened again. Mom came downstairs in the morning and I had to ask her what that was since I really didn't want to know those things about my parents. Turns out Rudy was rattling the door knob until the door popped open. In trotted Rudy with Maggie behind him. Mom had to put a suitcase behind the door, and it sort of dissuaded him in that pursuit.