It's human nature to delete unnecessarily repeated words in your head that appear on the page (or screen, in this case). Trust me; it's one of the most frequent errors I corrected as a copy editor. I had to train myself to spot them as often as possible; I'm sure I miss it occasionally.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"