'The Walking Dead' returned last night with the season 4 premiere, "30 Days Without An Accident" but it's the pending infection that has everyone on the edge of their seats.

The focus of the upcoming episode seems to be an infection that is hinted to be in the water.  Carl's friend Patrick eventually collapses in the shower, and reanimates as a walker, while the camera remains focused on a dripping shower head.

Perceptive viewers will remember that at the beginning of the episode, Rick started the show by splashing water on his face.  He also found a pig dead standing by the water trough, so there are a few clues leading to the cause of the infection.

What are your theories on the cause of the infected?