In 1997, the National Oceanic and Atmospheric Administration discovered an unusual, ultra-low-frequency sound emanating from a point off the southern coast of Chile. It was the loudest unidentified underwater sound ever recorded, detected by hydrophones 5,000 miles apart. It lasted for one minute and was never heard again.

The Bloop, a mesmerizing short documentary by Cara Cusumano, investigates this unknown phenomenon with Dr. Christopher Fox, Chief Scientist of the Acoustic Monitoring Project of NOAA’s Pacific Marine Environmental Lab. “I took it to the very classified innards of the United States Navy intelligence,” says Dr. Fox in the film. “It wasn’t theirs. It’s captivating because we don’t know what it was. I am glad there are still mysteries on earth and in the universe.”