A device for breaking a series of perforations or cuts to open a carton or otherwise separate materials connected by a frangible severance line includes a pair of fold lines that converge away from the severance line, a collapsible line perpendicular to severance line and between the pair of fold lines, and third fold line perpendicular to and intersecting the collapsible line. A tear in the severance line is initiated by applying pressure in vicinity of the intersection of the collapsible line and the third fold line, which causes the device to apply tension to the frangible line, which is further weakened by having an elongated perforation that it centered on the axis of tension, and neighboring perforations that are angled toward the axis of tension. The angle of each perforation with respect to the axis of tension preferably varies depending on its location relative to the axis of tension.