Some microbes lie in wait until their hosts unknowingly give them the signal to start multiplying and kill them

After more than two years of the COVID-19 pandemic, you might picture a virus as a nasty spiked ball—a mindless killer that gets into a cell and hijacks its machinery to create a gazillion copies of itself before bursting out. For many viruses, including the coronavirus that causes COVID-19, the "mindless killer" epithet is essentially true.