Rabies is a viral disease that affects the nervous system of mammals, including humans. It's usually spread through the saliva of an infected animal, often through a bite. Think of it like a chain reaction: if an animal is infected, it can pass the virus to another animal or human through a bite, and then that animal or human can spread it to others.
The incubation period of rabies, or the time it takes for the virus to show symptoms, can vary greatly. It can take anywhere from a few days to several months or even years for symptoms to appear. For example, if you're bitten by an infected animal, you might not show any symptoms for weeks or even months, but that doesn't mean the virus isn't working its way through your system.