Don't you remember the scene where Jesse went insane looking for the ricin cigarette? Walt created a dummy with salt instead of ricin in the vial. He went through an elaborate charade of "helping" Jesse find it when they miraculously "found" the dummy ricin cigarette in the Rumba robot vacuum cleaner?
Don't you remember Walt hiding the real ricin vial that he had stolen from Jesse in the electrical outlet in their bedroom?
Yeah, I remember that, but Jesse was told by the FBI agents that ricin wasn’t what caused Brock’s illness, so Jesse would have no reason to think that Walt used the ricin, as ricin was not involved, according to the doctors and FBI agents...
See ya’,
Ed