I don’t have the reference handy, but the gist is: They use pithed frogs, and they do not jump out of slowly heated water. Intact frogs do jump out, but you can’t know if that’s because of the heat or some other random frog thought. Frogs have really elaborate reflex systems (eg: wiping reflex ), and a pithed frog given a sudden, large noxious stimulation will do something a lot like a jump, but the neural pathways accommodate to a slowly changing stimulus and fail to elicit movement.