Second shot of the Arizona Black Rattlesnake (Crotalus cerberus at the Tucson Desert Museum :)

(copy/paste)
Some info from the placard: This snake is native to portions of Arizona and New Mexico. Eats small mammals, birds, and lizards. They change their appearance while growing AND can shift their background color from light to dark and back again! (sadly color change is not apparent in my particular set of photos :X )