The light source is supposed to be coming from just below the upper left corner, around the left side of the top of the chair. At least, that's how I pictured it when I was doing the lighting and shading.

Also if you can picture it, the scales on his tummy are supposed to be shinier... I was thinking of my snakes when I did that part. They are very scaly on their tops, but their bellies are smooth and shiny.

I never was very good at shading...I tried to improve it a bit though, any better?