Pretty Much Dead Already - S2-E7
Revealing mistake: Dale threatens to shoot Shane, and Shane walks right up to him until the barrel of Dale's rifle is against his chest. Just before Shane walks up to him, you can see the imprint of the rifle muzzle on Shane's shirt from an earlier take. (00:32:50)
Continuity mistake: At the crossroads, after Rick starts to walk away from Shane, Shane starts to tell the story of what happened with the outbreak. Rick pauses and is looking off to his right as he is in the blurry foreground with Shane talking behind him, looking towards the left of camera. The angle cuts to a view from behind Rick, and suddenly Rick has his head turned to his left now, but also towards the left of camera but from this angle. (00:16:43)
Answer: The walkers could have knocked them down more than once. There may have been another wave that knocked down the fence earlier and they're going to put it up again soon.
Captain Defenestrator