unbendable arm, n.All

Unbendable arm (n.) of ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠aikido: hold it rigid and a strong man bends it; hold it easily, eyes on a distant point, feeling water flow through it like a hose, and it will hardly bend.