From Absolom! Absalom! by William Faulkner:
There was something curious in the way they looked at one another, curious and quiet and profoundly intent, not at all as two young men might look at each other but almost as a youth and a very young girl might out of virginity itself -- a sort of hushed and naked searching, each look burdened with youth's immemorial obsession not with time's dragging weight which the old live with but its fluidity: the bright heels of all the lost moments of fifteen and sixteen.
Faulkner is a wonderful technician of the sentence, but I find his observations about human nature sometimes only a little above average. Not here. The fluidity of youthful moments is for me a very touching observation. Reminds me of Proust, with less romanticism.
I think what the sentence means is that the two characters are looking at each other with an earnestness and energy that comes from the youthful, innocent sense young people have that life has no special meaning from moment to moment -- it is "fluid.
The key to reading a Faulkner sentence is to understand that one sentence doesn't necessarily express only one thought or viewpoint. It may express several. The first half of the sentence, up to the dash, describes the way the two characters, Quentin and Shreve, are looking at one another. The second half is more Quentin's private idea, since the story is being told from Quentin's viewpoint. It expresses Quentin's feeling that the moment between them is slipping away even as it unfolds. This second half is not so much about his attitude towards Shreve as it is his own feeling about the moment. So I think the sentence starts out with a shared emotion between Quentin and Shreve, then slides into Quentin's viewpoint alone.
How do I know there is a viewpoint shift? I don't, but the sentiment gets too complicated and intimate to be an emotion unspoken yet shared between two people. So as it branches, or curls into a more refined thought after the dash, I think the feeling retracts into the mind of Quentin instead of being in the air between them.
Yeah, it's a tough nut to crack.