Euthanasia

[sirtalis]

Hey all, the other day I found an injured spiny lizard on my property. Our cat had injured it to the point of no return, I put it down by quickly crushing it between a cinder block and a 40 lb weight. This got me thinking about putting down one of my own pets, lets say one of your reptiles was injured and you knew that no matter what it would die in the next few hours, would you take it to the vet or attempt to do it yourself. I think crushing one of my pets would be a bit gruesome so what method would be easiest, I've used CO2 on rats before but wouldn't a reptile breathe too slow for that to be effective, would the animal spend twice as long as a small mammal? Sorry this is a biy controversial but I'm just interested what ya'll would do

(This is a hypothetical question fyi)