Model for attachment trajectory and triggering cue leading to SAC silencing of sister kinetochores. In the trajectory we mapped, the first kinetochore (K1; blue circle) lost Mad1 (green star) and satisfied the SAC near its pole. The second kinetochore (K2) laterally attached through CenpE (red motor), generating tension that can stabilize end-on attachment of K1, thereby helping K1 bypass tension-based inhibition of initial end-on attachments. Despite being able to transmit force and bear loads from the outer to inner kinetochore (Box 1; gold), this attachment does not induce Mad1 loss at K2. CenpE pulls the pair toward the metaphase plate, where K2 forms end-on microtubule attachments and rapidly loses Mad1. SAC satisfaction must be triggered by a geometry-specific cue unique to an end-on attachment that CenpE-based attachments (even persistent force-generating ones) cannot supply. This cue could, for example, be binding interactions specific to end-on attachments or deformation of a linkage that only bears a sufficient load in an end-on attachment (Box 2; gold).