A worldwide epidemic starts when humans cut down trees in an area inhabited by bats, forcing them to relocate. One bat carrying the virus dropped a piece of banana into a pig pen. One pig consumed the banana piece, and when it was slaughtered, the virus spread to the butcher's hands. The butcher did not wash his hands before he went to shake the hand of a guest, thus spreading the disease to the guest, who then spread it to other people.

Susie sings a song about how germs travel and how you can prevent yourself from getting sick. The song is accompanied by visuals to help improve understanding.

This clip discusses the importance of wearing masks and what masks do to protect others and ourselves. This clip also disccuses the spread of COVID-19 and how face masks are important in stopping the spread of viruses.

Hank discusses what we know about T cells and COVID-19 immunity. He talks about how a new theory, "herd immunity" in response to COVID-19 may not be the solution to the disease.

The team creates a model of the virus causing an epidemic to better understand how it behaves and affects human cells. The novel virus changes continually, so it is difficult for them to create a vaccine.