In the HBP movie, why does Snape see Harry just before he kills Dumbledore?

I think that little bit of scene was neatly done. For a few seconds, maybe a few minutes, Harry is on the verge of trusting Severus, which shows him then to stay quiet for his protection (once more, he's protecting Harry).

In the light of what is to happen a few minutos later, it adds madami drama as Harry's trust in Severus that had started building up with that gesture (Severus putting his finger on his own lips), downright crumbled right after that.

Movie narration obeys to other rules than book narration. You have to have something madami dramatic. That scene does convey that drama perfectly well.

Beyond what LadyNottingham and Persephone have sinabi -- which I agree with wholeheartedly -- I'd also like to point out that Dumbledore didn't even have Harry take the invisibility balabal with them to the cave.

Also, I thought the way they handled it in the movie stuck better with how they'd developed Severus and Harry's characters in the movie-verse. Harry isn't nearly as much of a fighter in the pelikula as he is in the books. Him going down under the stairs because "Dumbledore told me to and I trust Dumbledore" fits much better than him trying to fight. And with Severus, it was always "which side is he on, which side is he on, what's he going to do?" And him standing under the stairs, wand out, protecting Harry, only to go up the stairs and kill Dumbledore fit better with the quite, reserved Severus we see in the movies, as opposed to the active, emotional Severus we see in the books.

I think for the movie only audiences it tricked them for Deathly Hallows. sa pamamagitan ng Snape putting his finger to his lips and telling Harry to be quiet like he was going to go up and unleash hell on the Death Eaters- sets up the tone of frustration/confusion/hatred that Harry has toward Snape until he knows the truth. Because he went up their doing the exact opposite- he knew he had to with the unbreakable vow and Bellatrix watching him like a hawk.