Anyone can make friends these days, since the claims to friendship are usually based on "Hello" and a lunch; but the making of enemies, there is an art to that. It is infinitely harder to win enemies than friends, and harder still to hold on to them. Remember: the subject is real enemies, not just those pests of whom one thinks with a dull, bored ache from time to time, or those whose irritating presence makes one pine for Madagascar. A real enemy is in a different league. He is a hated hater, a mirror image of one's meanest desires. He wants to do unto you exactly as you would do unto him.
Such people are rare and valuable, and with the proper care and feeding they may last a lifetime. An enemy well nurtured is a joy forever. When he is not maligning you in public, he is maligning you in private; when he is not maligning you in private, he is contemplating doing so. Wherever he is, some assault against your person is being committed. Wherever he has been, your bones lie heaped. He is enormous. In your dreams his shoulders press against your skull. He himself never sleeps. There is too much mischief to be done, too many calumnies begging to be aired. And think: it is you who brought this creature into being. He lives and fumes solely for you.
No wonder, then, that writers have taken such pains to portray the power of certain enemies, that power being a testament to their heroes' own. Milton gave Satan the height of a colossus in order to emphasize the magnificence of his opponent. Similarly, Sir Arthur Conan Doyle had Holmes near quavering when Professor Moriarty first filled his doorway: "My nerves are fairly proof, Watson, but I must confess to a start when I saw the very man who had been so much in my thoughts standing there on my threshold. His appearance was quite familiar to me. He is extremely tall and thin, his forehead domes out in a white curve, and his two eyes are deeply sunken in his head." Not that enemies have to be great in physical stature; small people often make the very best. It is that they must be huge in the imagination, ubiquitous, ready to don disguises or change shape entirely. Perhaps the point that Satan wished to make by turning into a serpent is that if one is to be susceptible to enmity, he will find it in even the lowest forms.