sid I can't tell for sure from that video alone because I can't see the bone hierarchy and properties of the IK constraint, but it looks like the IK is simply not being applied due to Mix being set to 0, or other reasons. The reason why I guess so is that the center of the bone does not appear to be transparent. When the constraint is applied, the bone looks as if the center is hollowed out. However, the bone is too short and thin to be clearly visible. Could you please show me the bone hierarchy and IK settings?
