In qigong as well as all the internal arts, internal coordination is achieved within the frame of the tailbone sinking, the top of the head rising and the shoulders directly aligned with the hips so that the spine itself does not twist at all. This leaves all the internal organs free to move with the twisting and wrapping of the extremities.
This is just a small piece of a very large proccess and there are many different approaches to teaching this principle. Some teachers may treat it as 'advanced' and so many qigong movements neglect this principle. This is partly because it is possible to break the over all principle of internal coordination into smaller components and develop them independently. It is also partly because once the principle is thourghly integrated into ones movement it is possible to be internally connected in any type of movement, including freely twisting the spine.
In practice, internal coordination is usually combined with other teachings; for instance, pulsing the joints, opening the qi gates, and various hydrolic processes in the body.
If you focus your training on internal coordination your movement will be come more snake-like.