In a study by Elizabeth Loftus, subjects watched a film of an automobile accident, then answered a series of questions, including one asking them to estimate the speed of the cars. What factor affected the subjects' estimate of how fast the cars in the film were traveling?
The way the question was worded impacted the responses of different participants. Asking how fast the cars were going when they crashed into each other makes the witness give a higher speed than if crashed was substituted with bumped.