People behave differently when they know somebody is watching them. Researchers at a fac outside Chi raised t lighting o a produ line a output impr, so th lowered i again a output improved once more. The lighting was clearly not the cause. Something about being studied had changed the workers, and every study of human beings since has had to reckon with the same awkward difficulty. There is no obvious way to observe people who are unaware of being observed.

Type only the missing letters. Each box is one letter, and the number of boxes matches the letters that are missing.