Old Ironsides being overflown by the Blue Angels
Group Block zombies stop all survivors from advancing.
non-Group Block zombies only block the survivor they are engaged against.
Thanks Dan, that's what I thought.
BTW, you may want to add the links to the videos you made for this game. I found the live play videos very helpful and, frankly, it helped with my decision to get the game. You and your family looked like you were having a blast playing it.