Overthinking Highlander Immortality

Highlanders are immortals in that they do not die from any wound... except if their head is cut off. Which raises two interesting questions.

How much can be cut off before the head is considered removed? Cut off an arm or a leg, fine, people have survived that, so Highlanders can too. But how about cut them in half at the waist? Their heads are still around and intact, so they survive? How about through the rib cage? Just above the heart? Cut a Vee mark from their shoulders down, so some chest is there, is that all right? One inch below the neck? Half an inch?

And from the other direction, how much of their head can you cut off before it counts? The eyes and ears, fine. Top of their head? A bit of the brain? Random brain surgery? Everything above the medulla? Just on the spinal cord?

Which brings up the other question: how much head cut off counts as being cut off? Just cut the spinal cord? Just a nick on the neck? How about slicing through half the neck but leaving the other half alone? Is the Highlander fine then?

Some of these might have been answered in comics and such, but it does get quite silly when you think about it.

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