[BBQToadRibs2]

Wait, carbon dioxide I think. We exhale both, but more carbon dioxide if I’m remembering correctly. (Which I don’t know, lol)

[FoxInSocks]

You're correct, we exhale carbon dioxide. We don't exhale carbon monoxide; that's a product of incomplete combustion, like your dirty old car or gas stove or water heater.

Our bodies are very sensitive to external and internal levels of O₂ and CO₂. Cellular respiration and the production of CO₂ is a pretty interesting topic.