From what I remember, the story is a POV telling of someone describing an alien invasion in detail. As the story progresses, the aliens themselves are described by the narrator. However this is done in such a way as to obscure the fact that the narrator is describing humans who have invaded his/her home world (i.e. their skin was smooth and they had claws and teeth etc.)
Does anybody know of such a story?
Sealing this answer from @SQB's comment1, this looks like "Sentry" by Fredric Brown, which you can see at Project Gutenburg. It's a very short story, and there's not much 'progression' in the story, but it's still a possibility.
Here's the... well... second half of the story:
And then he saw one of them crawling toward him. He drew a bead and fired. The alien made that strange horrible sound they all make, then lay still.
He shuddered at the sound and sight of the alien lying there. One ought to be able to get used to them after a while, but he'd never been able to. Such repulsive creatures they were, with only two arms and two legs, ghastly white skins and no scales.
1Which was, strangely, not the question that this was closed as a duplicate of...
