Two days after tomorrow will be a Saturday. What day of the week was yesterday?

Tomorrow is one day ahead of today, and two days after that is three days ahead of today. So today plus three days is Saturday, which puts today on Wednesday. Yesterday was therefore Tuesday. The traps: Wednesday is today, the answer if you stop one step short of the question; Thursday comes from reading 'two days after tomorrow' as only two days ahead; Friday is simply the day before Saturday, with the shift back to today never made at all.