John Berry
My theory is that the doctors of the future will take advantage of the fact that, when a child is first born, the top of the infant's skull still has a large natural hole in it. Through the natural hole, the doctors of the future will implant chips inside the skulls of infants, and, as the children grow older, the natural hole (in the top of their skulls) will eventually "grow over", thereby permanently sealing the chips inside.
Jundy S. Tandog
Revelation 13: 16-18 - 16 It also forced all people, great and small, rich and poor, free and slave, to receive a mark on their right hands or on their foreheads, 17 so that they could not buy or sell unless they had the mark, which is the name of the beast or the number of its name. 18 This calls for wisdom. Let the person who has insight calculate the number of the beast, for it is the number of a man.[a] That number is 666.