Spinning or "wobbling" is a genetic "disorder" commonly found in spiders and spider combos mainly. Many people still debate if this "disorder" truly effects the snakes health but I don't belief an answer has been found yet.
Many Spiders will wobble back and forth or hold their bodies in strange positions that don't seem "normal".
A lot of owners normally note that this is likely to occur when the snake is exited or about to feed, I have never owned a spider myself and have never seen it but this picture shows a strange positions I mentioned earlier.
http://www.coreywoods.com/Misc/Spide...eHead_3666.jpg