Here's an easter egg for you guys. It only works if you know the shortest way to get to the engine room on "Death on the Mississippi" (because I don't have the energy to start taking screenies and **** to show you where it is).
Basically, run over there, and outside of the engine room there's stairs leading up to secondary entrance. From out of that door, one of the guards will be exiting. Knock him out (obviously without getting spotted) and drag him in the door he came out from. Now, immediately turn right, and drag him to the rail, and drop him over it.
Now, take the Gator gang member (one of 6) that's walking towards the engine room as a hostage, and get him to the same place (again, without getting spotted). But instead of turning directly to your right, turn directly to your left, and drop him over that rail.
Now, if you've done everything right, all the NPCs on the level will have turned into zombies.
That is, they will all move slowly towards you (using the animation that's normally used for drunk characters). If you shoot them down they will get up unless you shoot them in the head... and so on. Skins haven't been changed or anything, it's just the regular NPCs from that level... but it makes for pretty good zombie fun when all of the NPCs from the fancy part of the ship start moving slowly towards you, at the same time.