Moving before the 'pain comes on' is an inherent skill in aikido ukemi. It took me a while to understand this
Of course most aikido techniques have pain inherent in them, and inducing pain is a motivator to further movement/immobilisation.
A non aikido trained assailant will not instinctively move the same way as a skilled aikido, so are lible to 'feel' more pain if a technique is applied properly. However it is up to the aikidoka to 'regulate' the intensity of the technique so as not to cause damage ( unless absolutely neccessary
just a few thoughts