I really liked this. It was gripping right from the beginning, and portrayed Carnage just right. There's only two ways to write Carnage, and this is the good one. That first line of dialogue("It's Miller's tooth. His goddamn tooth") sounded like it came right out of a Stephen King story; it wouldn't surprise me in the least to discover you read a bunch of that while writing this.
The exchanges between Kasady and Kafka were lengthy, but entertaining. You've got quite a talent for writing dialogue. I'd like to especially commend you on your use of curse word with Kasady. Rather than dropping them randomly through the dialogue, you applied them in just the right places to produce the maximum impact.
Overall, well written and well conceived. Hope you write more!