# Get joint positions of right arm.
shoulder = skeleton.joints[8]
elbow = skeleton.joints[9]
wrist = skeleton.joints[10]
elbow_to_shoulder = norm(shoulder.pos - elbow.pos)
elbow_to_wrist = norm(wrist.pos - elbow.pos)
angle_radians = acos(dot(elbow_to_shoulder, elbow_to_wrist))