system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is Carbon Dioxide (CO2) not poisonous, but Carbon Monoxide (CO) is?
gpt
Both of them *displace* oxygen -- which is not good.  

But additionally, Carbon Monoxide can take the place of oxygen in your blood.  Hemoglobin will link to it instead of oxygen, leaving that hemoglobin unable to play its role of delivering oxygen to your body.