system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are prions considered infectious agents instead of toxins or other kind of hazardous material?
gpt
Prions are misfolded proteins that clump together in the brain and cause problems.

The reason they're considered "infectious" is because they cause other proteins to be misfolded as well. This is something we don't fully understand, but we know that introducing a small number of prions into an otherwise healthy brain will cause more and more proteins to be malignantly misfolded. The initial prions don't replicate like a bacteria or virus, but they force other proteins to start misbehaving like they do.