Grease may be one of the most beloved musicals of all time, but behind the catchy songs and colorful jackets lies a surprising collection of strange and little-known details. Many of the actors playing high school students were actually well into their twenties and thirties, giving the film its unintentionally exaggerated teen look. Even the upbeat soundtrack has quirks—some songs were added late in production, while others replaced darker numbers from the original stage musical to make the movie more family-friendly.

The weirdness didn’t stop there. The famous carnival finale was filmed during a brutal heatwave, causing cast members to faint between takes, and the black leather pants worn by Olivia Newton-John had to be sewn onto her each day because the zipper broke. From on-set mishaps to last-minute creative changes, Grease remains a cultural classic not just because of what made it to the screen—but because of all the bizarre behind-the-scenes moments fans are only now discovering.