My interpretation of this scenario flip-flops.

Since I will forget the experience (b), I sometimes interpret this question as being equivalent to whether I prefer having something minor happen to me (a) or something more serious happen to someone else (b). Then deciding how bad (a) would need to be before I choose (b) becomes a squirm-worthy ethical question.

Yet on alternating thoughts, I realize the choice is not as bad as choosing whether case (a) happens to me or case (b) happens to someone else because I still need to factor in that the other person will forget the torture after it happens, so it doesn't happen to them either. I might as well say it's happening to me. But this feels like rationalization to avoid having my fingernail taken off, which I really don't want either.

In the end, I'm just confused about it.