Machiavelli wants you to go wild.
Hang on: before you head out to Mardis Gras, listen to what he's saying. He doesn't mean that kind of wild; he wants you to get in touch with your animal nature. Sounds like hippy dippy tree-hugger stuff, right? Not quite.
Machiavelli associates humanity with being good law-abiding citizens, and bestiality with raw force and power. Because rulers have to sometimes bend the law a little, they have to use their animal sides. Everyone knows that, but Machiavelli can prove it. He writes,
In ancient times writers used fables to teach their leaders this lesson: they tell how Achilles and many other leaders were sent to the centaur Chiron to be fed and brought up under his discipline. This story of having a teacher who was half-man and half-beast obviously meant that a ruler had to be able to draw on both natures. If he had only one, he wouldn't survive. (18.2)
Obviously, indeed. Let's look at that a little more closely.
Since a ruler has to be part animal, what sort of animal should he be? A horse, like Chiron? Does it matter? Yes, of course it matters. Machiavelli has even chosen your animals for you already.
The ruler should be like the lion and the fox. See where he's going? Lions are all proud and regal. They are in your face and they will eat you all up—unless they're the Cowardly Lion from The Wizard of Oz. Foxes, on the other hand, run things behind the scenes. They're slick, tricky, suave. You want to be as sly as a fox, right?
But why does a ruler have to be both the lion and the fox? Well, "the lion can't defend itself against snares and the fox can't defend itself from wolves. So you have to play the fox to see the snares and the lion to scare off the wolves" (18.2). Teamwork: it works better when it's just two sides of your personality.
Like always, Machiavelli gives us a real-life example of what he means. Septimius Severus, the Roman Emperor, was a pretty foxy lion (not this guy, although he's got the foxy part down):
[H]e was feared and respected by all parties and he managed to avoid being hated by the army. It's hardly surprising, then, that despite being a new arrival he was able to hold so much power: his enormous reputation always protected him from the hatred people might otherwise have felt as a result of his pillage and violence. (19.16)
In other words, he used his awesome power to stun everyone into submission and then his foxy slyness to avoid being hated. Perfect.
But his son, Antoninus, couldn't get past being a lion. He was so war-loving and cruel that "after endless individual murders, he wiped out much of the population of Rome and all the people of Alexandria. At this point everybody really hated him and even those close to him began to get nervous so that in the end he was killed by a centurion while among his soldiers" (19.17). Looks like he got caught in a snare.