A perturbation of a string is a permutation, but with one m removed and one r and one b added. For example, perturbation is a perturbation of permutation.
Challenge!: I'll bake cookies for the first person who can generate a list of all the words in your words file that have at least one valid perturbation. (In this case, a "valid perturbation" is one that also appears in words. Perturbation is undefined for strings that don't have an m to begin with.)
Update, eleven hours later: Thank you for playing! Jesse 
jes5199 wins the cookies with his Ruby implementation. Peter pmb was hot on his heels with Python. Further versions welcome.
Without looking at Jes or Peter's code, Alex oniugnip and I each tried it ourselves. Alex had it in Python in 20 minutes or so (although he says Peter's is more concise). (Alex is working on a Scheme version now; I'm looking over his shoulder as we speak, and one of the things I see is:
(define test-words '("yarmulke" "parmalat" "aardvark" "chutzpah" "intersperse" "permute" "parmalat" "perturb"))
This is perhaps the best thing ever.)
Here's my Perl version (which took a couple of hours, because I'm a slow programmer) and output. My results match Alex's, but differ from Jesse's; it looks like we have different words. In mine, 2070 words have perturbations (wow; I was expecting maybe a hundred). There are 2735 perturbations in all. imitatively -> veritability is one of my favorites!
And I'm more and more envious of you Python kids. I like that you can print anything. And that you can .append to an array.
