This cake was actually made by one of our CC members (Jeanne aka on CC FromScratch) Please see this thread:
http://cakecentral.com/cake-decorating-ftopict-620771-bobble.html
If the thread doesn't help perhaps you could try PMing her and asking her nicely for more assistance???
on that site. she tells how she did it in the comments.. hth
here is what she wrote:
you can eat the whole thing. The only exception is the internal support system, but the head is cake and the body is rice cereal treats. 
The head is cake and the body is rice cereal treats because I didn't need that much cake. The tube is made from various PVC items and then covered in fancy foil so it didn't touch the cake. HTH's
The head is pivoting on a 1/2" wooden dowel that sticks up from the cake base. There is a tube in the head for the dowel to go into. HTH's
my suggestion would be to pm Jeanne, she is very helpful to anyone that asks for help.
It's a basic thing. Take out one of those medicine cups that dose 3-4 tsp and put it upside down on the end of a dowel and see it tilt from side to side. That is the basic idea. The actual things were purchaced from the hardware store and the inside of the pvc tube/cap is more rounded then the flat bottom of the medicine cup which helps it to rock instead of jump. Also if the cup/pvc tube cap is taller there is less wiggle room for tipping making look more like a slight bobble.
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