I have very flexible shoulders and can often accept a nice long pin as a welcomed stretch. However sometimes the person is unwittingly holding my hand, albeit lightly, in such a way that my very arthritic thumb, which is having an exacerbation, is in complete agony.
I asking the person about their experience of what happened after the fact and coming to an agreement about slowly working through their comfort zone. But it is incredibly presumptious to think you can read what, how, why and how a person is tapping and overrule their judgement.
Presumptuous? No. To train yourself and take responsibility for being aware of is part of Aikido. This means being aware at all times of what you are doing precisely and in total control so you know if what you are doing will cause pain or not. You know if the reaction fits the action. That's the level of awareness to reach for.
Secondly, by teaching the uke not to assume anything and training them to focus on what is actually happening then you are teaching them that they have a responsibility too. Both sides have that responsibility.
I would expect an uke with any responsibility to inform me of any unusual circumstances pertinent to the training ie: arthritic thumb.
Anyway, rest assured that if it was me I would be able to differentiate between real unexplained pain and drama.