[3klipze]

Spoiler!

Definitely it was Walt who poisoned the kid so that it made jesse turn on Gus. At that time, Jesse wasn't really on Walt's side to kill Gus, but not after the poisoning.. Also at the beginning of the previous episode, Walt is sitting near the table where the "lily of valley" plant stood. He span his revolver the gun pointed to the flower. We didn't see what he was looking at in our point of view, but I'm pretty sure it was the plant