JR North wrote:
CO (not CO2) is heavier than air, so the cats, being at floor level,
took the hit first. Just starting my car in the garage and driving out
sets off the CO detector upstairs; Dangerous stuff if you are in the
right (wrong) conditions.
JR
Dweller in the cellar

Check the atomic weights of C and O and then tell me again. :-)
one c and one O vs. two O
...lew...