A computer implemented method for use in animating parts of a virtual object in a virtual world, the method comprising obtaining joint data for each joint of a chain of joints associated with parts of a virtual object, joint data including length data defining a vector length for a vector from the joint to a next joint, the length data corresponding to a length of a part in the virtual world, the joint data for at least one joint including vector constraint data defining a rotational constraint for the vector; accessing data for a target curve defining target locations for the joints of the parts of the virtual object; and processing the joint data to rotate the vector for a joint towards a target location on the curve for a next joint in the chain; and if constraint data for the joint prevents the rotated vector from reaching the target location: set the vector angle for the joint at an angle dependent on the rotational constraint; and rotate an immediately preceding joint in the chain to move the vector for the joint towards the target location on the curve.