Many popular fast-food items were invented decades ago and remain unchanged. Chick-fil-A's chicken sandwich uses the chain's original recipe. Other fast-food chains have similar menu items from when they first opened.

Fast food workers have a front-row seat to everything that happens behind the counter, from how long items sit under heat lamps to how often fryers get cleaned. While most items are prepared safely, some consistently raise red flags for the employees who make them.

McDonald’s McDLT McDonald’s thought they had a genius idea with the McDLT—keeping the hot side hot and the cool side cool. The burger came in a double-sided Styrofoam container, separating the beef patty from the lettuce and tomato.