Perhaps to frighten birds away, or perhaps to propitiate the gods, it was the custom of ancient Roman vintners to hang little images of the face of Bacchus upon their vines, to be swung by the breeze and turned in all directions.
The supposition was that in whatever direction the faces were turned about, the crops would increase in fruitfulness in that portion of the vineyard.
Now the Latin word for face is os; for a little face this becomes oscillum, and it is true that little masks such as these were used as described. Some of the older etymologists concluded, therefore, that the Latin verb oscillo, which means to swing, was derived from the motion imparted to these oscilla by the breeze.
However, the majority of present-day scholars doubt this explanation, and prefer to say merely that our word oscillate is derived from oscillo, without attempting to decide the source of the Latin verb.