I am not sure if we tested this on ourselves if we would feel the same level of pain that they did. It's just my opinion, but after watching mine play for over 20 years I think they have a pretty high tolerance for pain. I have watched my dogs wack or bump themselves so hard that I am reduced to tears just seeing it, yet they jump back up and resume playing like they did not feel a thing. Of course when brushing their hair mine have always winced and yelped even when I was hardly touching them, so I guess their hair must hurt easily
Just so you know I did not say this to suggest shock collars on the small breedes, feeling the pain or not, to me it would still not be a good idea, but I have always wondered why dogs could wack themselves so hard and not seem to feel it, anyone else notice that