Another thing to keep in mind is some people just don't have a very high pain tolerance and some people just make funny faces for no reason what so ever. HAHA. In the first video posted, I didn't really take those expressions to be ones of pain, but that is just me.
As far as the second video, they look sluggish. There is one guy who I think makes a painful face and that may be for dramatic effect to benefit for the video, but for all we know someone could have stepped on his pinky toe when they were getting up....
It is true, in these situation, you have to ask how much ham
does the camera put on. People know they are on camera and will naturally or purposely play to the camera. Talk about ki, the camera has it.
Also, in these situations, the camera eye is a narrow one. It doesn't catch everything, but than again it can catch something the eye can miss. Then there is the obvious thing, the camera can be manipulated to show and hide.
I am not saying these videos are doing this. I am pointing out these things need to be considered when looking at a video.