The Departed : The rat at the end

I thought the rat was there, fearful, cautious but needing and wanting fresh air and a clear view of all surrounding, even the beautiful dome.

Rats are rats because they have to be
Just as humans are humans

But each creature, we are learning, seems to have a capacity for joy, for hope, for happiness.

What that is lost all turns bleak.

Is amazing in this movie.

He's really an awful character
The social climbing is so naked

And yet
You see how the boy he was took help for his mom and never looked back.
If he had help another way would he have been a better person?
Or a desperate hungry climber always just that?

Excellently set up.