You know, there were more than a few theories floating around the Internet this past week about who really poisoned Brock. Including one fairly reasoned and credible one that says Walt really did poison Brock, as a last resort to get Jesse back to a place where he would kill Gus. Personally, I don't think any of the theories are true. I think Brock found Jesse's cigarettes and dosed himself, and this here is just two men grasping at straws for two very different reasons. Jesse has to believe someone's more responsible for Brock maybe dying than he is. And Walt needs to find any way at all to keep Gus from killing him. Does that give Walt an excellent motivation to murder Brock? Sure. I just don't think he did.
Anyway, Walt continues to press Jesse to buy his version of events: Gus found out about their ricin plan from all the cameras in the lab. Today, while he and Tyrus were at work, Tyrus lifted the cig off of him while Jesse's stuff was in the locker. Walt's using what remains his best weapon: the fact that, deep down, Jesse still looks to him to be the smarter one. "THINK about it, Jesse," he says. "It makes sense!" Walt grabs Jesse's arm, puts the gun up to his forehead, and dares him to do it, if he's so certain. Maybe right now he's also playing on Jesse's trauma over shooting Gale. Betting he won't do it again. Either way, a trembling Jesse puts the gun down. He then marches to the door -- he's going to find Gus and kill him. Walt tells him not to go charging into certain death. Jesse: "I'm going to do this one way or another, Mr. White." Walt looks at his old protégée. "Then let me help."