To me the "coolest" feature is that it saves dormant copies in cells, so that even if there is no detectable virus in the blood, a few months after stopping taking anti-HIV drugs the virus will reappear. If you sample the virus right when the first spike reappears, you will see a bunch of different HIV virus types, essentially the history of each mutation on that person, as each virus strain saves its own copies... (soon after the strongest strain dominates)