Sebastian:
I thought that I would be next on both, but I wasn't.
That feeling is one of the hardest things to capture in a "witness" story. There is a parental type who is delivering at least one spanking - within hearing if not within sight of you - and odds are you are at least partly involved with the reason the spanking is happening. Maybe you were an accomplice, or it might have been your idea but you were smart enough not to do. Even if it's just "you should have stopped it" there's an almost shared feeling of guilt, and someone is paying for their role in that guilt by getting spanked.
A very hard feeling to capture in mere words.