If anyone has played Left 4 Dead, they'll immediately remember the humble Boomer. All 300 pounds of him shambling towards you, mouth full of vomit ready to spew all over you. When you shot him, he would explode and get vomit all over you, which in turn attracted all the nearby zombies to you. Given that we already have morbidly obese zombies in Diablo III (see the gameplay video), and that they explode into a mass of worms when killed, it doesn't seem a stretch to assume that they've gotten a vomit attack.
However, we have no idea what said vomit will actually do in game. Hell, we don't even know which zombie it's confined to. It may even turn out to be an ability shared by all zombies, though how this attack would differ from their normal physical attack is still up for debate. Personally, I would like to think that it will be a small armor debuff, think corrosive vomit. Though, if they do make it so the vomit attracts all nearby zombies, I'll be a happy camper, that's definitely a mechanic I'd like to see in Diablo III.
Now, if that wasn't enough to get you on the Left 4 Diablo bandwagon...
Official Blizzard Quote:
Diablo: High-priority task for our modelers this month: We have a critical shortage of demon corpses.
Think back to Diablo I and II, the three classes of monster were demon, undead, and animal. If they've got too few demon corpses, then surely they've been focusing on hordes of zombie corpses!
I don't know about you, but I think we've solved the fifth class debate with this as well.
It's totally going to be Francis.