Houses - The other side?

I approached the row of houses and noticed the same thing happening between each of them.

The windows, the doors, and anything that the undead could pass through was nailed with either wooden planks or with metal sheets. It didn't look like a typical house that was barricaded for the safety of the people inside but for the ones inside to never come out. I could already hear thuds, growls, and snarls coming from the rows of houses in front of me and I couldn't help but wonder who had the time to keep such a number of houses to be locked in like these.

As I took a closer look, I noticed that a black-green substance was starting to ooze out of the gaps of the wooden planks or the holes made by drilling in the metal sheets against the doors or the windows. I could hear each one of them trying to get out by clawing their hands against the barricades but it was to no avail.