It got a lot better on revision and I didn't even have to make it much longer. I didn't previously take into account what is almost a bound house-elf relationship Snape had with Dumbledore all those years. And like a house-elf, Snape doesn't know what to do with the idea of freedom from that, so he hasn't really thought about it. Here comes this crezy request and now all of those issues come to the fore, and he has to not only deal with this new idea, he has to decide where he stands, which is probably harder.