Wash immediately backs up at the first sign of movement, putting himself between the casing and Dipper. He's pretty sure this is bad fucking news, but he needs to know for sure. Deep in his gut he knows he's going to have to do this again, knows he's going to have to take the shot for the second time today, but he can't do it unless he's sure- he can't do it without confirmation-

And there it is.

He pulls the trigger twice as she- it starts to scream, putting two bullets straight through its head. That should have enough stopping power to buy them a little time, and that's all they need to get out-

And then his motion trackers come alive, radar filling with dozens of blips. That scream alerted every goddamn zombie in the vicinity and they need to move. He scoops Dipper up in one arm and sprints for everything he's worth back the way they came. "Move!"