If freezing is used as euthanasia the reptile MUST be cooled first, not put directly into the freezer. I was going to mention this earlier but didn't want to derail the thread as humane euthanasia tactics would be a good separate thread and I do believe has been discussed on this site before.
http://bio.biologists.org/content/ea.../18/bio.012179
It is not the *best* way but it is a way. Study was done in Australia for euthanasia of invasive cane toads.