While you and the Straw Hats were going to Thriller Bark, you then hear a menacing, haunting tune.

“Yohohoho, yoho-ho-ho! Yohohoho, yoho-ho-ho! Gather up the crew, it's time to drink the ship's brew, pirates we internally are challenging the sea! What's the waves to rest our heads, Ship us as our beds, Hoisted high upon the mast!”