One area of testing that often gets neglected are the various ways that bugs can be ferreted out by considering how they “hide.” Testing an application is sometimes like walking a mine field, where you have to trigger the mines in order to see where they are hidden. Another analogy might be a virus hunter, who has to find signs of an outbreak by testing the population, some of whom are hiding to cover up the fact that they have a virus. Here I want to present some information about why testers (and developers!) should consider a technique known as hidden-fault analysis and, more importantly, show how the notion of hidden faults can skew test results.