Tweening

Tweening is a technique to improve animations in RuneScape. Released in Animation Pack 1 in July 2009, it creates a smoother and better-to-look-at animation than before. Basically, two frames of animation are interpolated (blended together) to create a third frame inbetween them. This makes the animation appear smoother to the eye.

Here is a comparison, no tweening vs. with tweening: