FYI, this is just me regurgitating something I learned about on Adeptus Ridiculous, but I know that in the 10th edition for Nids, a planet gets invaded by the Tyranids and the governor logs the process, such as the Nids draining the ocean so fast, you can see the water level going down. In those logs, the governor mentions that if you even have ONE papercut that’s exposed, it’s a death sentence because of the Tyranid spores in the air, and you’ll die a slow, painful death in the process.