spotted something new: The arrows point to denser knots of material that are somehow causing the
reverse shock to move even more rapidly, and that material appears to be moving inward, not outward.
see WATCH THE EXPANSION OF THE CAS A SUPERNOVA REMNANT WITH YOUR OWN EYES!
https://www.syfy.com/syfy-wire/watch-the-expansion-of-the-cas-a-supernova-remnant-with-your-own-eyes
look at the video including the green arrows pointing at the accelerated Micro black holes ( former starspots: Q-FFF Theory)
see also: Primordial Black Holes and dual Herbig Haro Effects for Star-Galaxy formation.