Its a known phenomena that the human eyes and mind can pick up certain letters arranged in a any sequence. BUT - there is a key to all of this!!!!
If you notice carefully, all the correct letters are there, just arranged in a different sequence so the mind is able to , without you realising unscramble these letters into a sequence you recognise.
Geez the brain is great!!!!!
Read this:
"Subject: pwoerd of the hluan mlid"
It makes little sense as the words do not contain the correct letters to make the word correct.
Therefore, words with the correct letters in the word, although mis arranged are readable. Those with the incorrect letters become difficult to comprehend on the first pass which is what the mind looks for. 2nd and third passes may pick up the meaning but by then a previous statement, or the gist of the whole post maybe lost.