In the early days of the COVID-19 pandemic, scientists around the world felt an urgent need to understand SARS-CoV-2 so that effective therapeutics and vaccines could be rapidly developed. This led researchers to turn toward viral propagation in Vero cells as they had been previously used to culture other related coronaviruses. However, as our knowledge of the virus evolved, we learned that using Vero cells for propagation was not optimal for the novel coronavirus as cultivation on these cells led to the accumulation of mutations and deletions in the furin cleavage site of the spike protein, impacting pathogenicity. Thankfully, Calu-3 cells provide a solution.