Avoiding influenza is everyone’s top priority come flu season. Today we have the flu vaccination as the preferred (by most people) method for prevention, but you may be interested to know how a person sneezing near you can result in a fever, runny nose, cough, and sore throat. An animated video uploaded by NPR shows exactly how a virus invades our body and exposes our cells to the flu.

Surprisingly, it’s much like opening a locked door with the right key.

“When you get the flu, viruses turn your cells into tiny factories that help spread the disease,” the video description reads. “In this animation, NPR's Robert Krulwich and medical animator David Bolinsky explain how a flu virus can trick a single cell into making a million more viruses.”

According to the video, it only takes one virus particle to infiltrate our body before millions are replicated unwittingly by the nucleus of our cells. Thankfully, our bodies are home to around 100 trillion cells, meaning “a million viruses is just a drop in the bucket.” We also come equipped with a handy immune system capable of killing off any viruses it comes across.