An extremely thin wire or filament wrapped in a stasis field and attached to a handle typically resembling an oversized jump-rope handle. It can easily cut through most materials, and even hull metal with effort. It typically has a red bulb at the end to show where the tip is located. When not in use the wire is retracted into the handle. The original was discovered in a Slaver stasis box; Human manufactured copies were in use by 2645. In 2658 they had recently revolutionized Human society, bringing a return of dueling and swordplay on many worlds "The Soft Weapon", Neutron Star p. 83. [Spoiler alert: Ringworld]Speaker-To-Animals used a variable-sword in an attempt to hijack the Long Shot in 2850, at the start of the First Ringworld Expedition.
Reference: "A Relic of the Empire", "The Soft Weapon", Ringworld chs. 4-5
An alcoholic drink from Wunderland which in 2648 was said to taste like "a hand grenade with a minted sugar casing".