I can't stop long but had to drop in to share this with you...
I left the cat out after his breakfast he usually spends an hour or two out before coming back in. After half an hour the dog and I heard a slight tap on the letter box, thinking it was mail I go to the door but nothing was in the box so I opened the door and the cat trotted in, I couldn't believe it, he can actually tap the door to let me know he's there. Wow.
I had a St. Bernard who always came “knocking.” She was smart enough to learn that she could use her paw to hit the door really hard, letting us know she wants in or out.

Wow. Just. Wow...