When an infected animal bites you, the rabies virus sneaks into your body through the wound. It then travels to your brain, where it starts to multiply like crazy. At this point, you might start to feel a little off, but you won't know what's coming.
The early symptoms of rabies are pretty vague, which is part of the problem. You might feel a bit flu-ish, with a headache, fever, and some muscle weakness. But as the virus progresses, things start to get really weird.