I'm baffled completely by this version of the 3 Little Pigs. In the version I know, the phrase used over and over again is:
I'll huff, and I'll puff, and I'll blow your house down!
There was no sneezing involved. I think you've been reading some strange alternative version so it's hard to tell why the writer has used "huff", "snuff" and "sneeze".
As far as a doornail is concerned, it's not used for anything more than any other nail. It's a nail used in a door or a doorframe. You hit it with a hammer until it goes all the way in and it hold the wood together. This is one.