Most rituals that involved blood or pain were not as horrific as modern sensibilities could imagine. The Maya did not slaughter people and throw them into pits by the dozens. According to most of the information gleaned from the steles, the royal family offered their blood in recompense for the initial gift of blood by the gods when humankind was created. This occurred at special holidays and for particular purposes.
Any time people purposefully injure themselves enough to scatter blood around, it involves pain and a gruesomeness factor. Things like jade knives, stingray spines, and decorated spikes would make cuts or piercings. Women would pierce their tongues while men would pierce their genitals. In those very early days, you must wonder how many died of infections.