Zombies don't eat everything, they eat humans. Various zombie movies have taught us that zombies have some form of survival instinct, and they require human meat to live. 
I can't remember what it was called, or even when I saw it, but I remember seeing part of a bad zombie movie where they fall upon the house cat. 
So, at least in that case, it would be zombies eat all living flesh. 
Which is sort of what I meant. 
Not, like, a zombie gnawing on a tire swing. ;d 
...I once (really, just once) thought about wanting to eat a forearm. 
Really, it's just like a giant turkey leg. 
Perhaps the voodoo/scientific experiment brings out the the subliminal urges in the human brain, or our primal, caveman-like instinct to hunt things that run?