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1. In this version, Nan Xiren got poisoned because Zhu Cong, who was poisoned, wounded him and scratched his arm, transferring the poison over to him. That's why both Nan Xiren and Han Xiaoying (who was also injured by Zhu Cong) died with snake venom markings all over their bodies. Technically, we don't see Zhu Cong get bitten, we just see Ouyang Feng palm him, but Huang Rong's narration indicates that it was snake venom which kills him. I'm surprised that Han Xiaoying's venom still managed to spread all over her despite her suicide - she still looks normal when she slits her throat, so the poison must be one which still spreads across the body when the host is dead. Huang Rong calls Nan Xiren the "second shark", Yang Kang the "third shark", and Sha Tongtian the "fourth shark". In the novel, and in LOCH 83, Yang Kang is the "second shark". Of course, in this version, Nan Xiren's tongue is uninjured, and before he dies does manage to strain out a couple of "Jing Er"s. Why he didn't just say "Yang Kang" remains a plothole.
2. During the flashback, when Yang Kang is stuffing the jewels into Zhu Cong's clothing, Zhu Cong's arm gently falls and brushes Yang Kang's chest. In that moment, with his dying breath, he pickpocketed him.
I have no idea why they did the deaths this way, though - surely the way Zhu Cong, Han Xiaoying and Nan Xiren looked it was obvious that it was Ouyang Feng? Had Huang Rong never seen a snake poison victim before? Maybe it's more subtle in the novel (because Nan Xiren, at the very least, did indeed die of snake venom) but in this adaptation, snake venom victims look as obvious as the Joker's victims, and only someone blind couldn't tell that the three freaks died of snake venom. The only explanation is that nobody had ever seen a snake venom victim before, and I can't really remember any instance of anyone really dying from snake venom in LOCH prior to this scene, I guess.
One thing I DID like about this scene was that it was Han Baoju who wrote the unfinished word instead of Zhu Cong, and that he did it after seeing Ouyang Feng unmasked - because this means he really was writing "West", which was misinterpreted as "East". Going by LOCH 83 (and the novel too, although it's less obvious), when Zhu Cong wrote it, he technically didn't really know that it was Ouyang Feng behind the mask, and hence was probably REALLY writing "East". That would have made the entire clue redundant.