system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why carbon monoxide is so poisonous to breathe when carbon dioxide is not.
gpt
Carbon monoxide binds very strongly to hemoglobin, the molecule that carries oxygen in your blood. When it does so, it stops hemoglobin from binding to oxygen, and limits your body's capacity to get oxygen in the process.

Carbon dioxide, which is almost completely non-reactive, doesn't do that.