This storyline is used in the novel "The Killing Floor" by Craig diLouie. The "infection" that causes the zombie apocalypse is able to react to human defenses and evolve to defeat them. In one case this takes the form of a man who doesn't realize he's infected, whose purpose is to get amongst a crowd of humans at which point he unconsciously infects them. He gets into a FEMA camp, where his presence results in the population turning and the camp getting overrun.

If the slow turners are meant to play this Trojan Horse role what do you think would be their trigger to turn? Proximity to a large group of humans? A heavy concentration of sweat in the air? Wouldn't it make sense for them to turn suddenly, rather than going through a gradual transformation?

I'd love to hear more about that "slow turner" that they saw at the Colony.