The article from Mashable discusses Google's analysis of historical flight data to determine the cheapest days to fly within the U.S. and internationally. For domestic flights, Google found that flying on a Wednesday can save up to 15% compared to a Sunday, with the cheapest day to depart being Tuesday and the most expensive being Sunday. For international flights, flying out on a Tuesday or Wednesday can save up to 10% compared to a Friday or Saturday, with the cheapest day to depart being Wednesday and the most expensive being Sunday. The article also notes that these trends can vary by destination and time of year, and suggests using Google Flights' "Explore" feature to find the best deals.