From the discussion Engineer Valve gathered game controllers for the buttocks and tongue:

The second controller, designed for the tongue, must be placed in the mouth. It is assembled from a layer on the sky, to which an optical sensor with green backlight is attached. Presumably, objects on the screen can be moved using language movements. A special key on the language gamepad can be programmed for any game action.

Three months of playing on this controller and your wife will not leave you anywhere.