I noticed an annoying bug in the final demo project for this chapter. You can see from this gif that there is a bit of continuing deceleration after releasing the refresh trigger:
After pulling the hair out of my head for a while, I was able to narrow the problem to the specific case when pulling down to refresh where the lowest cell in the tableView dips out of the viewable area of the screen. In other words, running the iphone 7+ simulator, this problem doesn’t occur if I increase (20) or decrease (5) the number of cells in the table view.