The phrase “there’s a girl in a ship riddle” refers to a kind of riddle that presents a state of affairs involving a girl in a ship and challenges the listener to unravel the puzzle. The riddle typically entails wordplay, logical reasoning, or lateral considering to seek out the right reply.
One instance of a “there’s a girl in a ship riddle” is: “There’s a girl sitting in a ship rowing in the direction of the south. The wind is blowing to the east. Which approach is the smoke blowing?” The reply to this riddle is that there isn’t a smoke as a result of girls row, they don’t row boats.