The general relativistic expansion of the universe over 14-odd billion years has been explained again and again in popularisations, in standard texts and has been the subject of much discussion on this forum. Such expansion is "slow", meaning that to us it is quite imperceptible. We find it analagous to the "ordinary expansion" of a heated rod, where the (proper) separation of component atoms increases slowly with time. Folk often liken the universe's expansion to the blowing up of a balloon with pennies stuck to it. All this familiarity may make such expansion seem well understood. But consider instead a more extreme situation where general relativistic expansion is "fast", as in the inflationary episode. Here the proper separation of elements of mass/energy increases extremely rapidly. Their "proper separation velocities" are very large. And indeed (because this is an exponential process) so are their "proper separation accelerations". But in general relativity one does not talk of forces, and Newton's second law relating force to acceleration doesn't apply on a "global" scale. Instead, under these circumstances, we are told that all change --- that must include separation, velocity and acceleration --- is driven by "the inflaton potential" and how steeply this potential varies with "the inflaton field". This invention seems to me very like "the gravitational potential" and how steeply this potential varies with "the gravitational field"; more familiar factors that control the "ordinary" expansion of the universe. Do cosmologists just accept the inflaton and gravitational fields as given mysteries of nature? Or do they have a deeper level of understanding of these things?