At the end of the episode, Rick leans against one of the walls of Alexandria to listen to a walker on the other side. As he approaches the wall, the camera angle shows that he is walking through a grassy yard, but when the view switches to an aerial angle, Rick is standing on a street with a small grassy shoulder.
When Aaron is shooting those walkers in the field he fires twice in a row without cycling the action. His rifle is a Remington model 7 varmint rifle, which is a bolt action, not a semi-auto.
When Aaron shoots the walker in the field, we see the shot from behind the walker, and the brain material is splattered onto a clear screen in front of the camera.
In the opening scene, which takes place moments after the closing scene of episode 11, the sun is on the complete opposite side of Rick's group as they approach the gates.
From the Alexandrian's perspective, it makes no sense that a group found in such pathetic shape as Rick's (no home, transportation, supplies, food, or even water) would be given leadership positions in Alexandria - A group that was much more successful at building, gathering, and not losing numbers than Rick's group ever was.