Watching cats watching birds

I like these pictures not only because they feature the most adorable animals I know, but for their symbolism. They all feature two worlds; worlds that can be defined in many ways. They all feature a threshold, a doorway, a barricade. They each offer a glimpse of what is unreachable or at least longed for on the other side. How can we define the two worlds in these photos? Where the cats reside can be innocence, childhood, safety, inexperience, even entrapment, while the world beyond can be interpreted as evil, experience, maturity, danger, or freedom. Take any of their facial expressions and examine what they seem to be feeling, and the worlds change meaning with each different read on their perceptions. Are they resentful of the screen door in front of them or grateful for it? Can cats feel resentment and/or gratitude? I say hell yes.