One of the coolest snakes around is the hognose snake.  They are very docile and gentle, but have a whole host of fascinating behaviors, including this defensive bluff that makes them look like a little cobra.

Eastern Hognose Snake

Defensive behavior of Eastern hognose snake (Heterodon platyrhinos) (flattening head), Los Madrones Ranch in the Hill Country, Texas, USA.Canon 1Ds Mark III. I80 mm. 800 ISO. 1/40 sec. at f/8. EV + 1/3.