![The Walking Dead mistake picture](/images/screenshots/208000-208999/208346_sm.jpg)
Continuity mistake: When Beth is looking for a key in Officer Dawn's office, she encounters Joan lying dead in the office from bleeding out, apparently from suicide with a pair of surgical scissors. Her left hand is covered in blood. But when Officer Gorman enters the room and Joan starts to turn into a walker, the blood on her hand has disappeared.
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