its the CO carbon monoxide not the CO2 (carbon dioxide) in petrol exhaust fumes that puts a cat to "sleep" , its why people go to sleep in a car with a leaky exhaust, Carbon monoxide is insignificant in a diesel exhaust.
a modern petrol car still has plenty of CO to kill a cat
a lack of oxygen wont necessarily kill you, (and certainly wont kill a cat - what with 9 lives and all that ) heck I can breath in consecutive whole lungfuls of Helium, (albeit its an inert gas) to extol an oration of Donal Duck
what I dont get is all this about being "humane" in an attempt to kill a pest,
a viscious horrible pest at that,
Many more humans go thru a much more horrible death when left to languish in Nursing Homes for example, (or connected to life support.) Humane ... pigs arse !!
I'm with Jack Kavorchian on this one.
The only good cat is a dead one !

