A dynamic simulation and visual model of how the SARS CoV-2 Spike protein drives fusion of viral and cell membranes. Binding of the S1 spike trimer ‘cap’ to an ACE2 receptor triggers release of S1 and unveils the S2 trimer below. Extension of S2 leads to embedding of hydrophobic fusion regions into the host cell membrane. Once tethered to both viral and cell membranes, refolding of S2 on itself drives membrane fusion and release of the viral genome into the host cell cytoplasm.