It's Christmas morning, and little Johnny got everything he wanted; but there's still one unopened present. His parents, who are subconsciously afraid of the wrath of their six-year-old when unappeased, bought him a toy he didn't ask for. Eagerly, Johnny throws the wrapping paper off of what he finds
to be a bright red box.
"Wow, a Hot Wheels Raceway!" At the moment of his initial encounter with the toy, he senses that it's different from any other toy he's ever seen, but he pays his instincual qualm no attention.
Some time later, the toy car track is completely assembled. It's magnificent. Little Johnny has never seen a strip of plastic that was such an honor to behold. It had every toy-car-throttling element any juvenile could imagine; peaks, dives, bends, bat wings, and loop-de-loops.
On Johnny's involuntary census of the highest points of the awe-inspiring track, he counts five loop-de-loops, but the first one strikes him as odd for some reason that his underdeveloped mind cannot fully comprehend. This loop-de-loop is not the tallest, but is the first element in the course, coming right after a tall, steep descent.
At this point, others in the room, look at the arch, puzzled. They don't know what's wrong with it either, but it seems that there is a strange angle to it. They also dismiss it, resting easily in their post-holiday garb and spirit of jubilance.
Johhny readies the first car to tackle the whiplash-inducing course. He positions the unsuspecting toy car on the edge of the monstrous slope, only seconds away from the first ominous loop-de-loop. Johnny releases the car, and it plummets down the first sections of track. In these few moments, the basic flaw of the arch ahead becomes immedeately clear to Johnny's elders.
Johnny watches eagerly as the tiny care levels out, and begins the quick ascent of the left side of the loop, begins to curve backwards, and falls straight down on its roof, ignoring the grandeur of the rest of the track.
Johnny is upseted by the fact that, no matter how many times he tries, the car fails in the same way; the loop isn't circular. Where all the other loop-de-loops in the course are in the shape of a circular run of track, broken at one point and attatched to the rest of the track, the first one takes the form of a Moebius band and even though the track starts level and ends levels, the twist in the plastic is entirely unnavigable for toy cars.