No Sanctuary - S5-E1
Continuity mistake: At the start of the episode when Tyreese and Carol are walking down the railroad tracks towards Terminus, they encounter a herd of walkers coming out of the woods. One of the first walkers to cross the tracks is a male walker wearing a burgundy sweatshirt with a rip in the middle. When gunfire erupts at Terminus, the walkers turn their attention towards it. In the next shot when they start to head towards the sound, we see the same male walker now in the middle of the herd yet to cross the tracks, next shot after that, we again see him at the front of the pack.
No Sanctuary - S5-E1
Continuity mistake: Near the end when Rick thanks Tyreese, the cabin door is open after Tyreese had closed it as the group walked up. In next shot it is closed again.
No Sanctuary - S5-E1
Revealing mistake: When Sam has his throat slit, the location of the wound does not correlate with where the blade was shown to be slicing the skin.
No Sanctuary - S5-E1
Character mistake: When Gareth is questioning Rick about what was in the bag he hid in the woods, Rick replies a .44. Rick is referring to his Python, which is a .38 or .357, not a .44.
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