Nobody could tell.

There was just a wormy squirming of arms in the air--seemed to be a couple of dozen of them, all writhing at once, and it just made me dizzy to see them go." "Why, ma, I hadn't any difficulty.

There's two arms on each shoulder--" "There, now.

One arm on each shoulder belongs to each of the creatures, don't it?
For a person to have two arms on one shoulder wouldn't do him any good, would it?
Of course not.

Each has an arm on each shoulder.