Trying to use analogies to describe prions is hard. What it actually is is a certain type of misfolded protein. That happens all the time–that would be like the humans falling off the tightrope. It doesn’t usually affect other proteins, and it usually just makes that individual protein nonfunctional. But prion diseases are proteins that are misfolded in exactly the right way that they cause other proteins to misfold in exactly the same way, which causes other proteins to misfold the same way… It’s like kids playing zombie tag, except the kids are supposed to be doing taxes or something so they aren’t running away from the chasers, and for some reason as soon as they get tagged they play along and now your taxes never get done and also you die