‘Grumpiness’ and ‘grumbling’ aren’t the same

From The New Yorker: "It's natural to assume that grumpy people grumble. But grumpiness and grumbling aren't actually as related as they sound. "Grumpy," the O.E.D. suggests, derives from the word "grunt"— and, indeed, when you're grumpy, you often don't feel like talking. Eeyore doesn't grumble; Statler and Waldorf, the talkative old men in the Muppets, do. To grumble, you have to be articulate and social. In fact, in my experience, you're more likely to grumble when you're full of energy and in an extroverted mood."