H-Mover is very attractive. It has the movement in its spirit. It displays all the letters from left to right (as this is the order of reading). The letters slide in from the right, stop for a short while, and the slide out on the right. The movement is slowing and accelerating using a physical model. This makes the animations attractive.
The weapon of this CAPTCHA: The method is to hide the information. There is no frame in the animation where all letters are visible at once.