One of Atom Egoyan's intentions with the film was to explore absences in the human condition, in this case largely from the viewpoint of Simon who has grown up without his natural parents.
The character of Tom was originally written as being older. Scott Speedman had read the script in Los Angeles and insisted on meeting with Atom Egoyan. When the director met Speedman, he immediately revised his preconceptions about Tom's age and made him younger.
When Sabine arrives at the door, it is gently snowing and her black coat has some snow on it. Once she enters the house (a different set, her coat no longer has snow on it and the rate of snow, as seen through the window behind her, is at a much faster rate.
In the scene at the end of the film at his grandfather's empty lake house, Simon first unloaded the wooden Christmas figures from his duffel bag onto a pile of firewood on the end of the dock. He then went into his grandfather's workshop and sawed the scroll off of his mother's violin. With his phone, he took a picture of the severed scroll in his hand with the dock in the background, but the wooden Christmas figures now appear in the middle of the dock.
Simon: [class monologue]
Innocence is a hard thing to describe, it's like a scent, a thing which some people carry. And from the moment they found the bomb, the security officials knew my mother had nothing to do with it.
Simon: I think that this idea we get, that if you get to know someone, if you humanize them, it stops you from pulling the trigger or setting off the bomb or whatever, well that's just a myth we're taught, something we get from the movies. When the reality might be that's what actually inspires extreme action.