The tripods are great big machines, (but actually, they're not great at all.) Every place has a once a year date in the morning when a few kids in the city around the ages of 10-20 are offered to the tripods for a capping. When these metal caps are embedded into their skulls, from then on they are considered a man/woman, and no longer a child. But once they are capped, they no longer have a free mind. Their bodies serve the tripods,

Forever!