Regarding the question of why Kin didn't snap his neck (back on page 4 or 5): If you look in the archive to where she killed scorpkin, you will notice that she not only had a grip on scorpkin's neck, but also had wrapped herself around scorpkin's tail as well (
http://www.goblinscomic.com/09132011/). She was able to use her secondary grip on scorpkin as a brace, and break her neck by pulling the neck towards the tail into a position inconducive to connected vertebrae. When she has Psimax, all she has is his neck. She can twist, and pull him around, but he'll just flop around after her like a ragdoll. It would take some pretty fast, hard action to snap his neck (and while Kin's tail is strong, we don't have any indication that it is fast). That's my explanation, at any rate.
@Reads_Forums:
You are absolutely right that once Kin attacked Psimax she had to have something bad happen to her. However, while Thunt is constrained somewhat by natural human reaction to various storytelling techniques (not many people would have liked the anti-climax of Psimax dying so easily), he still has almost-absolute control over the story. He didn't have to put Kin in a position where she could attack Psimax. If he hadn't, she wouldn't have lost her tail. So it is perfectly acceptable to say "don't do a GRRM on us" (setting aside, for the moment, your perfectly reasonable assertion that GRRM is not the only storyteller to kill main characters).
Also, while I agree that Kin's actions are stupid, one could say the same thing about her actions in the upside-down forest when she essentially rolls into a ball of helpless, quivering snake-flesh. It certainly didn't help the situation, and it endangered her companions, who had to then rescue her useless behind. But in these situations, Kin is not making a reasoned, intelligent response, she is reacting in a highly irrational, emotionally-charged way to circumstances which trigger flashbacks to psychological trauma. I imagine that if you were to take Kin in one of her calmer moments and ask her if attacking Psimax was a smart thing to do, her response would have been in line with yours and mine: No, it was stupid.
Here's hoping for the best. While it is true that killing characters to evoke an emotional response in the reader can be used with great power in the hands of a good storyteller (which so far, I think Thunt qualifies as), if one heaps too much sadness on characters, it will start to distance readers from what is happening. No one wants to read a story where no one has a chance of achieving happiness. I'm not saying that Kin dying is going to tip the story over into that territory, but I will say that I am hoping that she survives (which makes me incredibly unique, you see
).