Probably because when skimming your brain can mistake DFHack for both duck and quack.
Did you konw tath yuor bairn's frist atetpmt at miakng snese of wrtiten lagnuage invloves only looikng at the fsirt and lsat letter, word lnghet, and which chrarectas are in bewteen, but not at all at the spcecfiic odrer of those crharactes in bteween the fitrs and last letetr?
If you try hard to read that sentence, you will pain your brain, but if you just skim over it you will notice you can in fact read it at first glance just fine.
EDIT: on an intersting side note, people with specific type of dyslexia can skim-read a garbled sentence like that just as fast and as well as the population average.
They just have trouble with putting the in between letters in the right order when writing.
EDIT2: nice excercise to get a feel for what dyslectic people have to go through when trying to write is to try and construct a garbled sentence like I did here. Make sure the first and last letter are not garbled, and make sure to use the exact same characters as the orginal word.
This puzzling is what dyslectic people have to go through when trying to write normally. I completely agree with allowing them extra time on tests and exams, like they get here in the Dutch school systems.