re: Someone explain the BB ending.

quote:

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If you're Jesse, that's a huge jump to come to that conclusion.

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From reddit:
Huell used the same brand of cigarettes as the last time he swiped them from Jesse, so Jesse made the immediate connection.
Jesse was already suspicious of Walt doing the poisoning in Season 4 when he put a gun to Walt's head.
Also, Walt was the one who originally put the idea in Jesse's head that he might have misplaced the ricin cigarette.
Also, Walt just happened to be with Jesse when they found the ricin cigarette.