A professor of clinical psychology at Victoria University in Wellington, New Zealand, included a lecture on crowd psychology in his annual course.
To illustrate mass hysteria, he regularly showed TV news footage of teenage crowds greeting the Beatles at the local airport in the 1960's.
The professor showed this film for many years because it was the best example of mass hysteria. However, one year , when he ran the footage, he heard squeals and bursts of laughter from his students.
When the film ended he asked what had caused the hilarity. Replied one student, "We recognized some of our mothers!"