It is very disturbing to me to think that our heritage as humans includes human sacrifice, however, for countless millenia such has been the case.  Here the obsidian knife of the ancient mayan culture is picture as a glyph.  Etznab. I used the colors of red for obvious reasons, and blue sky and water.  This glyph is number 18 in the tzolkin calendar from the information I have been able to retrieve off the internet.