Rumors had their own classic epidemiology. Each started with a single germinating event. Information spread from that point, mutating and interbreeding—a conical mass of threads, expanding into the future from the apex of their common birthplace. Eventually, of course, they'd wither and die; the cone would simply dissipate at its wide end, its permutations senescent and exhausted. There were exceptions, of course. Every now and then a single thread persisted, grew thick and gnarled and unkillable: conspiracy theories and urban legends, the hooks embedded in popular songs, the comforting Easter-bunny lies of religious doctrine. These were the memes: viral concepts, infections of conscious thought. Some flared and died like mayflies. Others lasted a thousand years or more, tricked billions into the endless propagation of parasitic half-truths.