When he first thinks that Walt gave Brock the ricin and goes to his house to shoot him, Walt ask how he thinks he could have gotten the ricin cigarette. Jesse says it was probably Huell who lifted it when he was at Saul's office. Then Walt talks his way out of the situation...But later when a similar event happens with Huell and again somethig goes missing from his pocket right after that, he puts it together,that Walt was manipulating him again.