Another thing about Jesse figuring out Huell and Saul took the cigarette is that he had already figured it out in season 4 but that's when Walter talked him out of it. So once he saw his weed was gone he was able to jump to the conclusion so fast.
JESSE: I had it. I had the cigarette with the ricin in my pack this morning. The last time I saw Brock was last night. And this morning I switched the cigarette into a new pack. There's no way Brock took it himself!
WALT: Jesse, you're not thinking clearly, listen, you said it yourself, that you had it this morning. Then when could I have possibly gotten it?
JESSE: You...you had Saul do it. Yeah. Yeah. I went to his office. He called me in, just had to see me today. His big man mountain bodyguard patted me down, that's when he must have stole it off me right? That's the plan, was that the plan?