It’s obvious that the bulldog in this video, at least to some extent, understands what he’s seeing on TV. Something bad is happening, and he doesn’t like it!
I recognized the movie: it’s John Carpenter’s remake of The Thing. All right, the dog doesn’t understand it’s not real. But that goes for an awful lot of people, too. Both these dogs grasp the point that what they’re seeing on the screen is a long way from being kosher. They’re smart!