The length of the digit bone,
measured in CATUnits.
Controls how much the
CATMotion affect the
digit bone. A value of 1.0 means that CATMotion has 100% effect.
A value of 0.0 turns CATMotion off for the selected digit. A value
of -0.5 would mean that DigitCurl would have half the effect in
the opposite direction.