The original model Famicom featured two game controllers, both of which were hardwired to the back of the console. The second controller lacked the START and SELECT buttons, but featured a small microphone. Relatively few games made use of this feature. The earliest produced Famicom units initially had square A and B buttons. This was changed to the <answer>circular</answer> designs because of the square buttons being caught in the controller casing when pressed down and glitches within the hardware causing the system to freeze occasionally while playing a game.
What shape did the A and B buttons eventually become?
circular