Karyn and I were having a discussion in the lab today over some of the great unresolved questions of our time and the one that really had us scratching our heads was, "Do zombies poo?"Now, zombies being a favourite subject of mine, I had to give this some thought. Here's my response:
If they eat flesh, and continue eating it for any length of time then all that stuff has to go somewhere, right? They don't regenerate so if they really existed would you just have to wait until they were all too full to move? Maybe that's why they're so slow?
Well, partly that depends on the zombie. After all, your classic Fulci-Zombie is supernatural, through and through, animated by curse or proximity to one of the Gates of Hell, or simple vengeance (the exception, amusingly enough, being Fulci's "Zombie", which was a sequel to Romero's "NotLD"). Romero-Zombie's, though, seem to be, well, more "natural" isn't the word, but at least less Hell related.
They also don't last long, usually. Either they are destroyed by someone or they simply rot away. In this case, there's not a lot of time for food to fill them up before they get, at the very least, a hole in their midsection (usually from all the idiots who don't seem to understand that anything other than a head-shot is a waste of ammo). Thus, the "full" zombie rarely happens.
Also, consider this: the "classic" zombie wants "brrraaaiiinnnsssss", which are 70-75% water. So, again, not much "food" to build up. Where does the water go? Well, that comes nearly full circle, but I would think that the excess fluid is simply absorbed into the body. After all, without it, the body would dry up completely, and since they seem to last pretty well, they must have some hydration (I doubt they drink Gatorade).
A variant thought is this: once awakened from death, the story always seems to be (in the case of "scientific" zombies, more Romero-style) that something has restimulated their brain and they are aware only of their most basic instincts, i.e. feeding (why this centers around brains is a bit of a mystery, but Romero-Zombies have been seen eating flesh, as well, so who cares). It's really not much of a stretch to believe that if basic instincts of survival are awake, then the mechanisms are, as well. After all, you have locomotion and instinctual fears (such as fire), why not gastrointestinal processing? Heck, Bub from "Day of the Dead" was able to use a gun, showing that not all zombies were completely mindless.
So, with this in mind, I think the final answer is that, until such time as a zombie gets a hole blown in him large enough for his food to simply fall out, he probably just shits his pants.
Yes, this is the kind of thing I do at 7:30 in the morning.