Jesse realizes that Saul Goodman’s bodyguard, Huell, stole his ricin cigarette back in Season 2. This leads Jesse to connect the dots and figure out that Hank was responsible for poisoning Brock, not Bogdan. As he pieces everything together, Jesse cries "sewers" because he remembers how Saul had his pot taken from him earlier that day—implying they could have also taken the ricin. This revelation pushes Jesse into a rage, leading him to confront Holly and eventually attempt to burn down Walt’s house. It’s a pivotal moment where Jesse finally understands the extent of Walt’s manipulation.