So we set up a mic in one of the empty rooms, and fooled around with some pitching tools that shift the pitch of your voice down, and started making zombie moans, groans, and grunts. It's not hard to imagine that this got really silly, really fast. We now have enough zombie-noise material to last a lifetime, much less one 1/2 hour episode. In addition, we recorded a bunch of monster-noises - something that we need surprisingly often, but have relatively few of. There's an art to mixing together bull roars, gorilla roars, tiger growls, lion noises, and so forth to make a good monster-y shriek.
But a lot of times we're looking for a specific reation from our monsters - like getting shot with a Magna-Cannon, for instance - or being confused, or angry or... well, all the things monsters are likely to feel when confronted by pesky heroes. So, we said things like, "Okay, here's my motivation. I'm a monster, and I don't really want to be fighting, but my dark overlord has forced me to. I just got hit in the gut, and I'm hurt, mad, and confused. Roll 'em."
Then, we did zombie group noises. This is harder than you might think. When recording an individual zombie noise, there's no one in the room, so you can screw up your face, hunch your shoulders - do whatever it takes to cut loose unself-consciously. But with everyone else in the room with you, it's much harder. Not because we weren't all perfectly willing to zombify with gusto - but rather because we kept craking each other up. We'd just get to a fever-pitch of groaning when someone would cover their face and turn away, trying to keep from laughing out loud. That would set a chain-reaction of the giggles off.
I wanted to add some monkey noises to the library, too - my monkey-shriek is peerless, don'tcha know. But by the time we were done with our zombie and monster noises, all of our throats were completely ragged and raw. Now I just want some nice tea with lemon, maybe.
But, you'll be able to hear my voice on a nationally broadcast cartoon. Okay, it'll be drowned out by a whole other horde of shuffling zombies - but the point is, it's there.