The Serenity ship from Firefly, which was created by Joss Whedon and gained a cult following, made a quick cameo appearance in Battlestar Galactica, a popular science fiction TV series created by Ronald D. Moore. The crossover happened in the season 4 episode titled "Someone to Watch Over Me."

The Serenity ship appeared in a brief scene where it was seen flying over the planet Caprica, which was the setting for the initial attack by the Cylons. The ship's appearance was a nod to the fans of Firefly and served as an Easter egg for those who were familiar with the show.

The Serenity ship, which was a Firefly-class transport ship, had a distinct appearance with its rustic and worn-down exterior. Its inclusion in Battlestar Galactica was a fun reference to the sci-fi genre and its passionate fans.

The use of Easter eggs and references to other shows or movies is a common practice in the entertainment industry, especially in science fiction. It not only shows a 'connection' between different fictional universes but also creates a sense of shared history and culture among fans.