Tips for working with spline IK handles

To ensure that the joint chain moves smoothly when you animate the spline IK curve, the joints in your joint chain should be close to each other (short bones).
Create a simple curve with no sharp bends to help make the joint chain move smoothly when you animate the curve. Use a small number of CVs.
When you add an IK spline handle to the skeleton of most creatures—including fish and snakes moving along a motion path—parent each IK spline start joint to a transform node or parent joint that’s not controlled by an IK spline handle. This makes the joint chain move with the transformations of the parent while avoiding unexpected joint flipping. See Prevent flipping in the spline IK chain.
If you’re working on a character with a root joint that rotates very little, for example, a swaying tree, you do not need to parent the start joint to a transform node or joint. The start joint can serve as the character’s root joint.
For a character such as a fish or snake moving along a motion path, if you create a handle that starts at a skeleton’s root, turn on Auto Create Root Axis when you create the IK spline handle. This prevents unexpected joint flipping as you animate the automatically created parent transform node along a motion path. Also turn off Auto Parent Curve.
If you create a handle that starts at a joint other than the skeleton’s root, turn on Auto Parent Curve and turn off Auto Create Root Axis so the handle’s curve and start joint move with the transformations of the parent joint.
When you manipulate a tail or neck parented to a spine, avoid moving the first CV of the curve for the tail or neck. Move the second CV minimally, preferably only along an imaginary line extending straight out from the end of the spine. Manipulate the other CVs freely. This technique ensures that the skin flows naturally where the spine meets the tail or neck.
Do not parent the curve to the start joint. This creates a dependency graph loop that causes the start joint to chase the curve as the curve moves. To detect such loops, use the MEL command cycleCheck -all. For more information, see Help > MEL Command Reference and the MEL guide.
Do not parent the curve to a transform node that uses that same curve as a motion path. In other words, don’t turn on Auto Create Root Axis and Auto Parent Curve if you want to put the transform node on that curve. This creates a dependency graph loop.
If you change an IK spline curve to a soft body, you can add dynamic forces to change the curve’s motion. For example, you can connect turbulence to the curve to create random, erratic motion.