what you need:
pliers
wire coat hanger
rubber band
huge button or cardboard disc
envelope

(1) break and mangle the hanger
use the pliers to break off a length of hanger. Bend the wire into this shape.

(2) string the rubber band through the button and over the wire
a piece of cardboard also works if you can't find a big button.

(3) wind it up
rotate the button several times.

(4) pack it up
with the rubber band still twisted, insert the "rattlesnake" into an envelope. Or, fold a piece of paper in half, put the snake in that and then put the whole thing in an envelope.

(5) label the package
you could also write something on the outside that'll make the gag even greater. What you write depends on who you give it to, so be creative.