Minecraft wiki entry for Door, associated text: A door can be used as a switchable barrier to entity movement. Although primarily used to block movement by mobs and players, a door can also be used to control the movement of boats (for example, a door placed in a two-wide water flow stops a boat when perpendicular to the flow, but allow it to move again when parallel), items and minecarts (a door can stop a falling item or minecart, then allow it to drop again when the door moves), etc.