The function of a knife is to kill by causing substantial hemorrhage. Does that make a knife an arrowhead?
Shoot an elephant with a single arrow, will it bleed to death? I still say functionality is not a valid test. I didn't say functionality was never a valid test. I said with respect to this determination that it is not a valid test. An example of a valid test of functionality, would be:
I hypothesize that this green liquid is a good substitute for human blood. A functional test is an obvious part of testing that hypothesis. It may be the same in every aspect,(including the constituent cells), except color, but until it fulfills the functions of blood, my hypothesis is not supported.
Does dried blood pass the functionality test for blood? If it doesn't, I suppose you would say it is not blood.
Is the piece of rock you're showing me shaped like a knife, or an awl? If it's shaped like an awl, as you say, then let's stay on topic and not go chasing red herrings. The function of an arrowhead also dictates that it must have a design the allows it to be bound to the end of a wooden shaft, and be small and light enough to be propelled by the bow. If it's a knife, it still fails.
I guess if it has words, it must be an argument. Do you want to continue the debate under those conditions?