Right, Jaime had just told him that his first wife was a genuinely innocent girl and not the whore he had in the end thought her to be. In the shock of this revelation, he lashes out at Jaime trying to hurt him as deeply as he can. Tough day for the Lannister family all around.
Littlefinger is a subtle planner. Pinning the king’s murder on Tyrion not only deflects attention onto a convenient patsy but also would end with Sansa widowed and thus able to be used in his further plans. I have no doubt that he intends for her to end up with him when all is said and done.
I haven’t read the books so I don’t know if this question is answered or not but:
What was the reason for using Sansa as the poison mule?
If Littlefinger planned to frame Tyrion just to get Sansa for himself wasn’t he placing her in needless danger? And what if she chose not to wear the hairnet/necklace? Wouldn’t it have just been easier for Olenna to bring the poison herself?
Yeah, it doesn’t make much sense. Other than I do vaguely recall some business about it not just being framing Tyrion but also framing Sansa as well - Cersei certainly thinks they were both responsible, I think.
By having the poison on Sansa it makes it pretty much impossible for her to stay in King’s Landing and blame Tyrion for the whole thing. Or worse, try to spill the truth to Cersei to save herself. Hard to do that when Olenna or LF can point out the missing poison gem from the hairnet.
Obviously her not wearing the hairnet would have been a problem, but I think knowing how much she wanted to escape and having Dontos make it clear that the hairnet was part of the plan pretty much guarantees she’d wear it.
I think Sansa was not an integral part of the plan, but more a side benefit (from the point of view of the Tyrells, at least). If she hadn’t worn the hairnet/necklace, the Tyrells would have found some other way to kill Joffrey (maybe they had some other backup poison standing by, or they would have done it later), though Littlefinger would still have whisked her away.
I would like to offer a completely alternate theory for the book version of the PW. I can’t speak to the TV version because it differed in a number of key ways, but here is, IMHO, a perfectly logical interpretation of events and what they mean:
The poison was not in the wine, but in the pie.
When Master Cressen drank the laced wine, Melisandre spoke only one sentence before Cressen’s throat closed up.
Joffrey’s timeline is quite different. First, he drinks the supposedly laced wine after the chalice had been sitting on the high table throughout the entire pie-cutting ceremony. Margaery then tells him to return to the table because Lord Buckler wants to make a toast. Joffrey then says “My uncle has not eaten his pie.”
Joffrey then reaches down a grabs a piece of Tyrion’s pie and shoves it in his mouth, and says, “It’s ill luck not to eat the pie.” So here we have two full sentences and a pie-grabbing and still no reaction to the poison. Is it because it is more diluted in the large chalice rather than Cressen’s (actually Lord Davos’) small cup? Maybe, but then look what happens.
He spits out a few flakes of crust and coughs. He notices the pie is dry. He grabs another handful of pie and takes another drink of wine. This is when the first big cough happens, and the rest is history.
Is it possible that the reason the pie was dry was that the crystal had started to react with whatever moisture was available in the pie? Or that the first violent reaction to the poison happened because Joffrey had just added wine to the mixture in his mouth, instantly dissolving the crystal and delivering a concentrated dose of the poison down his throat?
I’m not asking if this is a certainty, but is it a possibility? But if true, wouldn’t that mean the Joffrey’s death at the PW was purely accidental, and the real target for the poison was Tyrion?