I havent read all the reponses but seriously the most humane way to kill any reptile is by crushing the skull...Ive had to kill rabbits and seriously a blow to the back of the skull kills them so quick they never knew what happened, especially if you pet them and get them good and calm first..Since freezing takes alot of time it cant be that good, easy for the owner cause he doesnt have to look and see the death therefore its easier not to feel bad...CO2 works great on rodents and I use this method if I have to deal with live rats but it still takes more time then crushing the skull...I have a relative that has goats, he shoots them in the head to kill them, they stand there grazing on some bushes and bang they drop down without ever knowing what hit them...SPEED-Humane....If I were going to die Id prefer lethal injection but if that is not available just shoot me in the head...Big Key is doing it right the first time though, dont want something flopping around half dead thats not humane....Believe me though I dont feel good about killing anything and it gets easier but not better...