The scales on a rattlesnake's back have ridges running down the center of them. The ridges are called keels.
Patterns on rattlesnakes often help to hide them, by making them look like the ground they are laying on.
Every time a rattlesnake shed its skin, it adds a new section to its rattle. For this specific reason some people think that is how you tell the age of a rattlesnake, but sections often break off so it is not really possible to tell their age from that part of their body.
Nobody knows why rattlesnake scales have keels. They may help to make the scales stronger. Or they may make the scales less shiny, by breaking up the light that hits the scales. This would make the snakes harder to see.