In season 3 of Breaking Bad, towards the end of the season, Jesse learns that Combo was killed by two guys that are working for Gus. He tries to convince Walt to give/make the ricin so that he would put it in the hamburgers that Wendy would then deliver to their car.
But Walt never agrees to such plot, and refuses to cooperate. Then Jesse says:
I will do it with, or without you.
And then we see Walt and Saul trying to figure out a way to keep Jessie from committing his plan. While at the same time, Jesse is confirming the plan with Wendy. The next day, we see Jesse and Wendy waiting for the two guys to show up. They have hambrugers with them. It is inferred that these hamburgers will lead to the death of the two guys.
Where did Jesse obtain the poison from? Did he make it himself? Is it a different kind of poison? (highly doubted since he confirms to Wendy that it is untraceable, thus it must be risen) Did Walt give it to him (even reluctantly)? but then, why give him the poison and then plan to have him arrested?
It does not make sense...