The Weegecules go into a body via the bloodstream. While not in a bloodstream, these molecules will remain still, however, once contact with blood is made, they quickly go up the stream and hijack red blood cells, and give them the Weegee Virus. This spreads throughout the whole bloodstream. A short while later, they go into the person's brain, and the Weegee Virus is transmitted to it. It tells the body to allow the Weegee Virus through it and then they turn into a weegee.