The artwork within the city of Chichen Itza is a bit different from that of Tulum due to the influence of the Toltec culture. This is actually a hypothesized relation, however I suggest that you read about and look up the photography of the Toltec city of Tula Hidalgo for a rich comparison to Chichen Itza. In any case the more violent ceremonial traditions came after the onset of the hypothesized Toltec influence. Ceremonies began to involve more and more human sacrifices rather than just animals. This relief depicts a priest carrying the detached head of a sacrifice. What you cannot see is the neighboring relief that depicts an eagle holding the sacrifices heart as if it were speaking through it. This gives an idea of the relation that these ceremonial rights had with the body of the sacrifice.