One of the trickiest things to do with a zombie tale is to decide the origin.  Whether viral or supernatural, the why never seems to be as interesting as the what or how.

Perhaps, this time will be different.

According to a video found on YouTube by IGN, video game fans will get to see the origins of the Valve game series Left 4 Dead (a personal favorite), but in a special expansion to an existing title from a different developer.

Overkill Software, developers of PayDay: The Heist briefly released a video earlier today showcasing a new level, called “NO MERCY”.  This level is set in the Mercy Hospital found in Left 4 Dead, and as the video shows, things seem to break bad real fast.

This could be really cool for both PayDay and Left 4 Dead fans.  I am left wondering, however - is this the first time two video games have crossed over, in canon?

Source: IGN.