I re-watched this with the subtitles on. After the Doctor offers his memories, he goes on his knees, and said something like "I can't feed you" (very quietly). I dont know if he realized it was not possible, or if he decided he did not want to do it.
Then, Clara offered the leaf and the Doctor commented on how powerful the potential energy was. I don't know if that is going to come up again this season, but I immediately thought of the weeping angels.