I dunno. I still think that the symbolism is far more fluid than implied by our discussions -- that there's consistency to the imagery, and that that makes it very effective on an emotional and intuitive level, but that the movie is not a patchwork quilt of symbols stitched together to make a Meaning.
At the risk of becoming boring: I second everything Katherine has said.
This movie
is full of symbolism, mirror scenes, bookends etc. But noticing, trying to understand and particulary discussing them is a tightrope walk. And the chance that sometimes we become too far-fetched is absolutely given.
But the good thing is, for all of us it is something different what s/he considers as plausible, non-important or too far-fetched.
I can see nothing wrong in contemplating
what Ang Lee could have meant with his milk and water picture. Maybe it was just an incidental remark of him, maybe he doesn't remember himself. But the chances are as good that he indeed did have something particular in his mind saying it. We'll never know for sure (like thousand other things regarding BBM) and that's part of the magic and of the fun.
Doesn't hurt anybody to ramble about it, does it?