We instinctively know when someone’s lying to us. That’s why, when you tell your significant other “no, I don’t think you’ve ballooned up, that button that just popped off your pants must’ve been defective,” they squint a little and stare into your eyes. They aren’t conscious of what they’re doing, but part of their brain is measuring your eye movements. At that moment, they’ve become a human lie detector. It’s part of the whole “survival of the fittest” thing. We’re all descended from the people who lived until they were fertile because they didn’t fall prey to liars. It probably began when every caveman who fell for the “no, there’s no sabre tooth bison charging at you” practical joke died off.

There’s a helpful diagram online. If you visit that page and go to the “Up and to the left” section, and then look at 0:47 of this Youtube clip, you’ll notice Michael Steele is auditioning for the diagram’s live action adaptation:

The lesson, of course, is every time your S.O. asks if he/she’s porked up a little — or every time you go on national TV and pretend your cowardly capitulation to Rush Limbaugh was part of some chessmaster-like strategy — put on sunglasses before you answer. They’ll never know you’re hiding anything.