In these verses, suddenly everything goes in slow motion, with the narrator offering precise detail: “left hand...sword...right thigh......thrust…belly…hilt…blade…fat…dung.” The whole narrative has been building toward this, and though it happens very quickly, but the text describes it in slow motion. The narrator (and the Holy Spirit) want us to get all the details.
21 And Ehud reached with his left hand, took the sword from his right thigh, and thrust it into his belly.