It’s called a Mobius strip.
Nineteenth-century mathematician August Ferdinand Mobius didn’t invent it, he just studied it closely.
I’ve always been fascinated by the thing. It’s simple: make like you’re creating loops for a paper garland, get distracted, and tape the wrong edges together. Like so:
Notify the HR department.
Now take two drawing implements of differing colours. Use one to draw a line down the centre of the loop’s outside, and the other to draw a line down the centre of its inside. Draw until the colour meets its starting point.
Correct: black inside, blue outside. Mobius: Blue.
As you can see, the Mobius strip isn’t behaving very well: one colour did both sides before meeting itself.
Never mind. You’ve decided these loops are too wide for the garland. Snip them along their freshly-drawn centre lines, then, to make two loops.
Correct: two loops of regulation width and diameter. Mobius: one loop of regulation width, double diameter.
Maybe the scissors aren’t feeling too well today? Let’s try that once more, just to be sure.
Correct: four slimline loops, comprising two coloured and two plain. Mobius: One double-diameter slimline plain loop twined with one double-diameter slimline coloured loop.
Uh-oh. The garland department union is crying foul, because the Mobius loop received only one cut while the regulation loops were given two cuts, one for each loop. The union demands that each of the two Mobius loops be cut, to keep pace with the proper loops. Here goes:
We’ve ended up with three double-slim, double-diameter, plain loops intertwined with one double-slim, double-diameter, coloured loop. Kinda pretty, isn’t it?
As for you four, excellent job! To reward you, we promise to cut and retape only three of you in order to proceed with the fabrication of slimline garland.