This is a disturbing episode that leaves the audience with a lot to think about. We lose some characters, gain some characters, and begin to learn who some of the others really are. We also learn some things we wish we didn’t know.
It’s hard to say which box is meant to be the titular box in this episode full of sinister and confining boxes. There’s the box containing Henry’s police file, which Pangborn tried to conveniently lose many years before as part of a deliberate cover up. There’s Matthew Deaver’s coffin, which makes a grand entrance through town on the back of a truck, straight past his widow, who definitely didn’t want to see him back in town.
There’s the many boxes that make up the prison, from the cells to the surveillance room to the camera monitors to the watchtowers. There’s the boxes that Zalewski and the other guards will be buried in. And the wooden box that Josef Desjardins has in his backyard with a cereal bowl and spoon locked inside that could have held Henry, Kid, or both at some point.
Then there are all of the mental and metaphorical boxes that the characters put themselves and each other in. Zalewski asked how one town can look the other way so much. The answer is partially that they all live in boxes with high walls and no windows. They avoid climbing up high enough to look over the top to check on anyone else.