IF the marks above and below the ligature (still in place at autopsy) were from JonBenét's nails scratching her own neck while she fought to remove the strangling, painful cord, it would seem to me that at least for SOME part of the strangulation activity, she was conscious. There are indications that the cord may have been relaxed and then tightened again. If that is true, then she may have struggled with the cord at the first tightening, received the hit to the head, went unconscious for the final tightening.

For the head blow, then, to be considered a 'mercy blow', I'd have to ask "when" was mercy excercised? It certainly wasn't during the sexual assault, nor during some part of the strangulation.

But, you have a good point ... WHEN and WHY was the head blow executed?