I tend to agree with Froot about the BG, but if the snake is on the ground then it becomes really hard to blur out the background. Try placing it on a branch which is in a beer bottle (and not directly in a beer bottle as Mongoose suggested
), and then try to blur out the BG. Here are some theoretical values for the depth of field using a 300mm lens (like I see you have been using) at 1.5m and also at 3m
1.5m:
F5.6 - 8.4mm
F8 - 12mm
F16 - 24mm
F20 - 30mm
F25 - 37mm
3m:
F5.6 - 33.6mm
F8 - 48mm
F16 - 96mm
F20 - 120mm
F25 - 150mm
So if you only want the head in focus and you are 1.5m away, you need about 30mm or maybe a bit more of acceptable focus, and thus F20 will work well (like you used). If using a 50mm lens, then you have to be 6 times closer but your depth of field stays the same. This can obviously be experimented with as well but it is more fun being a geek and working it out mathematically
. Maybe try getting a black background by using F25 or F32, a flash and make sure the actual background is relatively far away. I've said enough now...
We must remember that a photograph can hold just as much as we put into it, and no one has ever approached the full possibilities of the medium - Ansel Adams