Smarties is the first engine we developed. The CAPTCHA simply displays the characters from left to right, one by one. Display of the characters is not discrete, the characters fade. While playing with the engine, an additional parameter called offset was introduced that lets the characters start fading in earlier (not to wait until the previous character faded out). This resulted in an attractive moving animation.
The name Smarties came from the set of the random colors, and the funny font we chose for testing.
The weapon of this CAPTCHA: The method is to hide the information. As you see, the is no frame in the animation where all the letters are visible at once.