It is true you have to rotate an electron twice to get back to the start. It is called S2 symmetry. You can tell I enjoy the maths but I admit the explanation is terrible. The best I can do is that the electron is like a sock or glove that can be pulled inside out. In truth there is no easy way of getting to the mathematics at least that I know off. MP4 recording     MP3 recording -- -- Your browser does not support the audio element.