http://www.youtube.com/watch?v=CoJFePnJECA 

ok so 0:05 Milton states "the whole town is out on the street" to which it then goes to Andrea running with a gun.

At 0:06 seconds when Andrea's running who can hear a man sceaming. from 0:05 to 0:06.

Walkers must be in Woodbury and attacking the man.

SPOILER....

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Like those pictures showed us of Walkers in Woodbury.