... The Metaphysics of The Fly. (Hat tip, Dave Lull.)
I'm not sure about whether or not dogs (or cats) can reason. When I found my late cat Pandora, she was a kitten and I was house-sitting for a friend who was a ballet director. In the living room of his house was a large ballet mirror. One day, soon after she moved in, Pandora noticed a cat image in the mirror. She scratched at the glass with her paw, then went into the next room (the door to which was right beside the mirror) to determine if the cat she saw was in the other room. Having determined that whatever it was she was seeing was no real cat, she never looked in the mirror again. Seemed pretty reasonable to me.