This is a sentence from a novel which I do not understand its meaning. What is a whirling machine? and does it relate to scratching eyebrow? Or it is just an idiom? The setting of the story is around 1940.
It's a reference to the complex brain activity that must take place for a simple human action to occur.
The teacher(?) is implying that the children are stupid. That a machine (the brain) has to labour just to tell them to scratch their eyebrows!
