At the tip of the tail a rattlesnake carries a specialised scale called the button. Every time the snake sheds, the outermost layer over that region is retained rather than discarded, adding a loose interlocking segment. Shaking the tail knocks the hollow segments against one another at high frequency to produce the buzz.
Because snakes shed several times a year when growing well and less often when food is scarce, segment count tracks moulting history, not calendar age. Segments also snap off against rocks and burrow walls, so long rattles are uncommon in wild animals. The widespread belief that each segment equals one year is simply wrong.
The eastern diamondback is the largest rattlesnake, with reliably documented specimens over two metres, and depends on fire-maintained longleaf pine habitat that has been reduced to a small fraction of its historical extent. Its range-wide population trend is a live conservation question, and its status has been debated by United States federal wildlife authorities.