Originally Posted by niko
I don't get what happened.
The cigarette pack was not switched at all, there's no need to because in episode two of season five, Walter tricks Jesse into believe that the ricin cigarette was sucked up by the roomba. That cigarette has a vial of salt in it, because Walt wasn't just gonna give the ricin back to Jesse. The vial of ricin is the electrical socket in Walt's bedroom.
Jesse has obviously been becoming more wary of trusting Walt, realizing just how often he is manipulated by Walt, and his suspicions from season four (about Huell lifting the ricin cigarette off of him at Saul's office) were only confirmed when he realized that his weed had been lifted from his jacket by Huell as he was leaving. That made it click in his head that he was right the first time around in season four, when he had the gun pointed at Walt's head, assuming he was the one who poisoned Brock.
No, he was not poisoned by the ricin, obviously. But the ricin cigarette missing was the catalyst that set Jesse on a path for revenge, against whoever poisoned Brock, and Walt manipulated him into believing that was Gus Fring. It doesn't matter that it was lily of the valley, the missing ricin cigarette is what matters, because it was the tool used to set Jesse off. Jesse knows how smart Walt is, and knows that he is capable of coming up with a plan that complex, using a plant that creates symptoms incredibly similar to the effects of ricin.