Sometime when I'm tired, I'd rather make hand gestures (like an instinct in me) than opening my mouth and pronouncing sounds/intelligible words. I wonder which of the 2 requires more energy to our body. As I read that swinging our arms when walking costs us 10% energy less than non swinging them, I also wonder why, in the case that moving hands/fingers costs us less than talking, we didn't develop such a skill. A bit off topic: maybe obese people should try not to swing their arms when walking? Edit: Have you experienced the same feeling, i.e. wanting to make gestures instead of talking? I do experience it several times a week. I don't know why, but I'm very tired although I sleep about 8 hours a day and in a somewhat good bed.