Oh my Lord.(spoilers)
That's an ending I didn't see coming in a million years. Not since "The Long Good Friday" (which also involves broken glass to the jugular).
Anyway, the final scene really pulled up this flick from 'ok ' to 'friggin great', and now that I look back on it, the whole script was tight enough to hold up on repeat viewings. The way their relationship is subtlety foreshadowed throughout was great.
I thought it had a great message; that motherhood and maternal instincts can be corrupted, by that way of life. And it's the youth that pay the price.
I think I'll forever be wondering if her crying over her sons body were momentarily real, or were just another facade that she was pretending to act, even though no one was watching. Was it just a freak accident, or was she always ready to kill him? Disturbing.
Limit of the Willing Suspension of Disbelief: directly proportional to its awesomeness.