Why do we call our biceps guns? The slang lexicographer Jonathon Green suggests that the metaphor first pops up in baseball around the 1920s, when players referred to their throwing arms as guns. Believe it or not, the early baseball pitchers actually threw the ball intending for the batter to hit it. It wasn’t until later that a strong arm, or gun, was needed to throw a pitch too fast to hit. This is part of a complete episode.