I should be receiving a Noble Prize for this one soon, if not at least a KFC discounts booklet. There is an irresistible force in the universe, stronger than gravity and probably comingling with quantum energy. This irresistible force draws every human who's ever walked by a display cannon to stick his or her head in the barrel. See the incredible photo below for evidence!
As you can see, neither the diameter of the cannon nor the size of the human head can overcome this irresistible force. This chap was outfitted with anti-stickheadincannongear (see small knapsack on back) and was still unable to resist The Force.
In my early study of this phenomenon, I had presumed that the ratio of height of cannon to height of person would reduce the strength of the Irresistible Force. I was indeed surprised to find that I was wrong, despite the strong mathematical predictions suggesting the opposite.
I had been toiling for over three years studying this freak of nature, as I called it when I initially encountered it, though my mother-in-law thought I was referring to her, which I was, sometimes, when I was informed that an obscure amateur scientist had begun a similar investigation years ago, when the earth was black and white, but failed to proceed further in his studies since he used himself as the cannoneed subject, and furthermore was unawares that the cannon depicted here was not a display cannon but rather a live one that was shortly thereafter employed to distract the enemy's flanks, leaving behind only shreds of experimental notes and an old buy one get one free Dairy Queen coupon.