That persistent cough that comes with your flu or those itchy red spots that you get with the chicken pox aren’t just a nuisance for you: Without those symptoms, your virus wouldn’t be able to find its way to a new host so quickly.

Coughing, sneezing, and itchiness are all signs that a virus has finished its incubation period inside your body and is ready to conquer new territory. But just how long does an infection spend inside a host before it tries to break out? Life Noggin is here to answer the question with its latest video. After watching its explanation of the behavior of viruses below, check out our list of the deadliest viruses from history.

[h/t Life Noggin]