² What if the anesthetic only paralyzes the salamanders and they merely can't display signs of agony? I lived with this unpleasant thought for many years, until a graduate student in my lab began probing salamander brains for electrical activity in response to tactile and visual stimulation. He found, to my relief, that MS 222, at concentrations that immobilize the animals, turns off stimuli-related electrical activity of the brain.

[3] The salamander embryo's midbrain regenerates; see Detwiler, 1948.