1. After claiming she's off to "grab a taxi", Isabelle first walks over to Dirk, and Christine spots them make out behind her back [Perhaps "making out" is a bit strong-- would they do that knowing Christine might possibly catch them in the act? It would be enough for Christine to merely spot a glimpse of Dirk in the area where Isabelle is headed to put two and two together.]
2. Genuinely hurt, she gazes after the couple walking up the stairs towards the exit [Or perhaps the first frame shows her watching Isabelle leave, while the second frame shows her spotting Dirk just managing to head toward the exit at the top of the stairs, as Isabelle is still climbing]
3. Being who she is, Christine quickly regains her composure
4. …and ominously plots revenge!

Patrick's fourth frame reading would perhaps indicate why these shots may have been cut from the final film. They might make it too obvious to the viewer when, the next morning, Christine tells Isabelle the story of her sister. As it stands, Christine's attempt to bond with Isabelle in this scene seems perhaps genuine. But had it come after the deleted shots above from the Bode Museum, the viewer might immediately sense that Christine is lying and plotting revenge. In this same scene, of course, Christine turns on Dirk, as well, and in between, makes it (almost confusingly) clear that she is aware of something going on between Dirk and Isabelle.

However, it has always seemed to me that in De Palma's film, Christine is more hurt by Isabelle's leap-frogging taking away of her plans for New York than for any indiscretions she may have had with Dirk. By leaving out the shots above, the viewer is left to speculate whether or not it was always part of Christine's weird scheming to put Isabelle and Dirk together-- and who knows, maybe even with the deleted shots above, maybe she had, in fact, meant for the two of them to have a fling. Going back to The Black Dahlia, think about the New Year's eve party, in which Lee watches Bucky and Kay kiss each other, and De Palma's camera focuses on Lee watching them, his feelings on the matter difficult for the viewer to discern. Has Lee been plotting for these two to be together? Has Christine been doing the same? De Palma sets up the long looks from Christine in Passion's opening minutes, as Christine watches Isabelle leave her house after wrapping Dirk's scarf around her neck. Is she already thinking of a Dirk offering this early on? It might explain a few things, but no it doesn't.

ALAIN BERGALA ON 'OBSESSION'
In "Time Denied: An Apotheosis of the Imaginary", Alain Bergala looks at the assumption of the image in De Palma's Obsession. "The major difference between Scottie in Vertigo and Michael in Obsession, states Bergala, "is that Michael is in a deeper sleep than Scottie. He wants to believe in the reality of his waking dream with a deep and naïve conviction. The whole film is an obstinate refusal to wake up, to leave the bliss of the imaginary. He rushes like a bull towards the first illusion that is offered to him – this woman who is the reincarnation of his dead wife."

In one section of the essay, Bergala discusses how De Palma's camera movements in Obsession follow the slowness of Stanley Kubrick's in Barry Lyndon: "A slow zoom-in draws the viewer into the bottomless pit of the imaginary. In Samuel Blumenfeld and Laurent Vachaud’s book of interviews, De Palma talks about the Kubrick of Barry Lyndon (1975), of the slowness of that film, of ‘the impression that everything was happening in slow motion: the movements of the camera and the actors. You really got the feeling of perceiving time in a different way, as if we had actually returned to the 18th century’. In the same interview, he claims, regarding the zooms that are used systematically in that film, that he would be bored, personally, to repeat the same technique throughout an entire film. And yet this is what he does tirelessly in Obsession, where he multiplies the long, fluid shots of the undulating imaginary."

"RESPONSIVE EYES AND CROSSING LINES"
In the fourth essay, "Responsive Eyes and Crossing Lines: Forty Years of Looking and Reading", Helen Grace presents an episodic look at her experience within the landscape of feminism over the years. In episode 3, she recalls the protests against De Palma's Dressed To Kill while in London in 1980:

"We saw Dressed to Kill, fearing that we would be shocked and horrified, and that we might come out convinced that screen terrorism was necessary. Instead, we watched a film which seemed to say more about masculine anxiety than about the fears that women were expressing in relation to the film. We kept waiting for the horror – and when it came, we enjoyed it. We wondered if we had seen the same film that people had been complaining about, so we went to one of the street meetings to discuss our problems. We found out that, in fact, none of the women had seen the film at all, and they did not want to hear our opinions about it.

"And this turned out to be a general feature in every situation in which a ‘citizen censorship’ movement called for the boycott of a film to which one group or another took offence, whether it was feminists and gays objecting to a Brian De Palma film, or Christians protesting the screening of Jean-Luc Godard’s Hail Mary (1985) five or six years later. It was exactly this period of the ‘80s when some strands of feminism seemed indistinguishable from right-wing Christian extremism in the anti-democratic gestures of, for example the Dworkin-MacKinnon Anti-Pornography Civil Rights Ordinance (1983) – which, fortunately, did not succeed. In any case, it was anti-pornography activism that first drew my attention to Dressed to Kill. And that is how I came to be a De Palma fan."