You need to crop out the distracting green line (the grass?) in the background. It draws the eye away from the subject.
You ought to try experimenting with your "approach angle" as well. Sometimes this exact shot has much more "life" if you are a little in front of the animal shooting the head from an angle, rather than straight on from the side. Of course, this is easy to talk about, difficult to do with a captive snake that won't stop crawling.