Very nice. I don't usually go for the one-shot either, not if there's no plot to move it along (or particularly hot sex), but this is a great theme and nicely imaged. I especially like, from a thematic sense, the bit about rats; that's an excellent rationale and nice that in their fear and pain he's almost rewarding himself. Self-flagellation.

I also like how although you use long, complex sentences, you break it up once in awhile with a fragment (the good kind). It makes the narrative flow much better, makes the reader come up short without stopping completely.