Earlier I wondered about missing bugs because your mind does not expect them, like a gorilla running across the screen. Later, I plan on writing about some more research from this area of cognitive psychology, but recently I ran into an example. A tester opened a ticket about an error message which should not have occured. The only thing was, the error message had a grammatical error in it. When the tester reported the error message in the defect report, he corrected the grammar.