Yup.
Instantaneous brain destruction would be the most humane at home euthanasia method. So smashing or crushing the head....
Vets will use anesthesia overdose or cardiac puncture.
Co2 is considered cruel due reptiles going through periods of apnea. They don't need much oxygen to survive and can go long periods without it. It could take hours to put down a reptile via co2, which could be agonizing. And a reptile could potentially survive a co2 chamber.
Decapitation is also not humane. The head can still be alive and feel pain up to 30+ minutes after its been cut off.
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