This is a video created by Redditor midwesternhousewives highlighting a nodding bearded man in the first row behind the boxing ring, a previously unknown visual clue for when to punch Piston Honda or Bald Bull the second time you face them to score a TKO when they're charging (the visual clue in the first round against Bald Bull is a camera flash on the right side of the audience). So, there you have it, after all these years. Now not to brag or anything, but I discovered a secret to Mike Tyson's Punch-Out over twenty years ago. And that secret is that when you're playing if you yell at the game loud enough and throw your controller at the TV your mom will ground you and hide the Nintendo.
Keep going for the video.
Thanks to everyone who sent this, all of whom are presumably playing Punch-Out right now staring at faces in the audience.