Why? Well, because retroviruses are these special viruses that contain reverse transcriptase and what this enzyme does is it essentially reverse transcribes the RNA molecule into the DNA molecule. And once we produce that viral double stranded DNA molecule in that cell that viral double strand DNA molecule is injected. It is incorporated into the cell's genome to produce something called a provirus or a proviral DNA. The profiral DNA is the genome, it's the DNA of that whole cell that has incorporated that viral DNA that we injected. And the great thing about these retroviruses is most of the time they don't actually kill that cell, at least not immediately.