The conversation with "Iris" in the cavern toward the very end of the last day of investigations for the last case feels very different on a second play through. You notice things you may have missed the first time. This is, of course, because you know that she's actually Dahlia.
*"Iris" promises to do everything she can to help solve the locks, but is probably insincere.
*Even though it had been pointed out the previous day, "Iris" doesn't seem to know about the contradiction between her testimony and Bikini's until you "remind" her. "Iris" also doesn't remember giving you the hood until you mention it. She seems to determine where she was before lights out through logic rather than memory.
*During the magatama unlock sequence, "Iris" makes underhanded insults (of the kind where it seems like she didn't mean for it to be offensive, but she did) if you get the wrong answers. One response, where she says something like "I feel sorry for you and your confusion because you can't figure anything out," leaves Phoenix thinking "I didn't know she could be so harsh!" Her sarcastic comments asking you to "show me something you are 100 percent sure about, okay" if you show her the silhouette profile are just like her sarcasm when Mia cross-examines her.
*After the psyche-unlock, the part where she says "my sister [Dahlia] always does the right thing" is even more laughable once you know that it's a stealth boast rather than naïveté. The part where she tearfully admits to betraying her sister is actually a harsh accusation that Iris betrayed her - which the hypocrite may be using as her internal justification for having just locked her sister inside a freezing and unstable cavern. When she tells her sob story about how after the diamond theft, Dahlia was "destined" to be trapped into doing the things that lead to her execution (even though Dahlia actually had several times when she could have limited bloodshed without putting herself in much danger), it's her 100th attempt at winning sympathy. When she talks about how Dahlia stole the diamond for revenge because their dad treated their mom badly, she's explaining and trying to justify herself.
*Finally, when Phoenix asks "Iris" if Dahlia ever talked about her college boyfriend, "Iris" replies, "she told me she hated his guts." This is Dahlia taking a snipe shot at Phoenix's heart while pretending that she's only repeating something she heard without realizing that it referred to him.

:phoenix: :There’s only one reason! One as obvious as sister Bikini in a bikini!

For example, that THIS IS SPARTA reffrence totaly cought me off guard XD