sdwr already explained this very well in their sibling comment: The extra dimension is another direction that you can move in, apart from the three directions y

sdwr already explained this very well in their sibling comment: The extra dimension is another direction that you can move in, apart from the three directions you're already familiar with. A piece of penne doesn't provide you with such an extra direction because movement along the penne can still be described by a tuple of 3-dimensional position + velocity vectors.