What is the word harpoon referring to in song lyrics from Bobby McGee?

The word "harpoon" in the song lyrics "Bobby McGee" refers to a spear with a barbed tip, usually attached to a long rope, that is used for spearing large fish, such as whales or seals. In the context of the song, it is used as a metaphor for something sharp and painful that can cause great damage or harm, like a heartbreak.