Zombies hearts don't beat and so the blood would be congealing inside them and there would be no mechanism to remove the digested material about the body to fuel it or remove waste products. I would also guess that their digestive system was similarly switched off. I see the eating as being instinct and not functional, the zombies seen to swarm people so it is possible that they only ingest small amounts per zombie anyway.
You can fix ignorance, you can't fix stupid.
Tinkety Tonk and down with the Nazis.
