I just finished the anime last night. I also rewatched the last episodes (22,23,24). The last time I watched an episode of the anime, I noticed that there's a relation between the events that happened in ep 24 and 1. Here's what I think. Okabe saved Kurisu by piercing himself for the blood pool so that the present Okabe (talking about the ep 1) will see/mistake her as dead in the first episode.(re watch from ep 24 to 1 to see the connection) The scream in episode 1 was definitely Okabe's (the Okabe from ep 24 when he pierced himself). Although it also doesn't really make sense to me on how the D-mail was sent to Daru in episode 1. Causing Kurisu not to remember meeting Okabe. And herself being alive (refering to ep 2)
After thinking about stuff regarding the REAL plot of the whole anime series, I realized that in the first episode, Kurisu wasn't really dead. Okabe in the first episode mistook her as dead, which is exactly what Okabe in the episode 24 wanted. The first D-mail which Okabe ( 1st ep ) sent to Daru: "Seems someone stabbed Makise Kurisu." ( I forgot the exact words)
That caused the "misunderstanding", wherein, if Okabe went back to the time where the D-mail/Phone Microwave didn't exist, Kurisu would be dead, which wasn't.
It's a pretty interesting topic, and I'd love to hear and see your opinions regarding this discussion. Especially those who just finished the one of the greatest anime ever, welcome to the fandom ^^
Note: If anyone have corrections for my post/theory and stuff , feel free to reply