see here's the thing (no pun intended)...
obviously, Thing has an unbelievably high amount of damage soak and can take punishment at unhear of levels... I mean you only need to see his boubt with Champion to understand something as fundamental as that.. but when wolverine hit him, he bypassed straight through things exterior.. to his interior.. he mangled the insides of the thing where thing isn't used to taking abuse..
THIS at least is consistent with wolverine's claws vs. things skin.. yeah thing hit wolverine away after wolverine slashed at his face, but then he doubled over in pain.. later.. when he was fighting a giant robot he even put on a mask but when the robot hit him in the face he screamed out in pain such that no one had ever heard him do so before...
torture is kind of different, with time you're mind slowly begins to accept pain as it is given, or accept the fact that you ARE in pain.. something akin to this is sprained ankles...
yeah if you already HAVE a sprained ankle but you're aware of it and have some descipline you can easily keep up and walking/running with the right mind set.. but at that moment when you sprain the ankle the shock to your nervous system and your brain are both too instantious for you to do anything but fall over.. same thing applies to this feat...
again.. for it to TRULY be PIS there has to be multiple examples of thing getting scewered up to 3 times in a single sitting without going down.. otherwise PIS is nothing more than a copout here like it usually is...
and capt is right about the nerve cluster part... but that's only if you REALLY want to rationalize what happened...