Last (but not least!), we peel up an action-packed ribbon cable. All told we uncover:

Two more IR LEDs—bringing the per-controller total up to 24, the exact number found in the Vive controller.

An LED that shines through the top of the controller, presumably as a visible light status LED.

A final switch for the Oculus or menu buttons, depending on which controller you're looking at.

A spring contact for the conducting pad that turns the "thumb rest" into a capacitive button.