Tzab is the Maya name for the Pleiades and it means the rattle of a rattlesnake. The identification is one of the easier ones to accept on sight: the cluster is a small tight group of faint points, and the segments of a rattle are a small tight group of pale rings.
The rattlesnake is not merely a hazard in Maya thought. It appears in iconography with feathers, in the sky, and in association with rain and with the ancestors, and putting its rattle overhead places the animal there by implication, its body running along the sky.
The cluster's zenith passage is one of the events Mesoamerican observers tracked deliberately. At the latitude of much of the Maya area the Pleiades pass directly overhead, and the passage falls near the beginning of the rainy season, which makes it agriculturally useful in the same way the Arabian and Polynesian uses are.
The Aztec use of the same cluster is better documented and is more dramatic. The New Fire ceremony at the close of the fifty-two year calendar round turned on the Pleiades crossing the zenith at midnight, which was taken as the sign that the world would continue, and fires across the empire were extinguished and relit from a single new one.