What's the smartest thing your pet has done? This is specifically geared towards cats and dogs, but if another type of pet's story is relative go ahead.
Also, how smart do you see dogs and cats to be? The general consensus is that dogs only mature to a two and a half year old human's intelligence, but sometimes I don't really agree.
One day my dog hadn't had a meal in some time, and we forgot about it, so she picked up a tissue from the bathroom garbage can (I assume; it could have been from somewhere else) and put it in here food-bowl, then whined. It can't be a coincidence because she's done it more than once since then. (Not that we don't feed her enough; she seems to get hungry between meal times.)