Basically, in viral __________ , the company thinks of a(n) _________ , interesting ________ —it has to be ___________ so that __________ will want to tell it to their ___________ straight away. In this way, the people become the advertising ___________ . This is much ________ than expensive TV time slots or space in a(n) ___________ . Here's an example. Google, when they first marketed gmail, their e-mail __________ , made it invitation only. Anyone who got a(n) __________ could give away more invitations to their friends.