How to make a moebius bagel

George W. Hart devised an elegant, mathematical way to slice a bagel [AIR 16:1]:

It is not hard to cut a bagel into two equal halves which are linked like two links of a chain.

The line ABCDA, which goes smoothly through all four key points, is the cut line. As it goes 360 degrees around the Z axis, it also goes 360 degrees around the bagel.