Histogram showing the distribution of velocity ratios. The top panel represents every pair from a simulation using Corespray, and the bottom panel shows all the pairs in our observational data. The vertical dashed line shows a critical ratio of two. Theory predicts that it is very likely that RS-RBs have velocity ratios greater than two, as can be seen in the simulated data set. On the other hand, the observational data show that more than half of the pairs have velocity ratios of less than two.