Union Square was full of zombies this morning.

Not real ones, admittedly, but actors dressed in torn, bloodied clothing, with white painted faces spattered in blood.

They were part of a brilliant guerilla campaign for AMC’s new show, Walking Dead, which sent zombies out on the town in 26 cities around the country – a relatively low cost way to drive buzz for the series across the news world and the blogosphere.

In Union Square, the zombies drew quite a crowd: onlookers laughing, tweeting, shooting the scene with phone-cams.

But, weirdly enough, the Zombies and I also rode the subway together, starting up at 49th St., when a dozen of them and I both boarded the same car of a downtown R train.

The zombies stayed in character for the whole ride, staggering around, drooling, making odd noises. But in the train, they pulled a totally different reaction. By and large, the riders completely ignored them.

Problem is, staggering, drooling, and odd noises don’t stand out much on a New York subway, where mentally ill homeless are a too common part of the morning commute.

Perhaps it’s a sign of the terrible desensitization – even dehumanization – inherent in city life. But zombies and the homeless apparently fall in the same category for most New Yorkers – something we don’t want to think about, at least when trapped together awkwardly in the enclosed space of a subway car.

On a train, we don’t have the luxury of physical distance, so we create it psychologically – we avoid eye contact, make overly casual displays of looking around everywhere else. If we all collectively ignore someone, we seem to think, it almost means they don’t even exist.