Perhaps you've seen the swinging reptile tail avatar on several different accounts here on FA. But every one of them has a fundamental flaw -- they're animated backwards. They all have the tail wagging the butt, instead of the proper model of the butt wagging the tail. As an example, take a look at  jamescorck's original avatar, and then look at this corrected one made from his. Note the action of the tail relative to the walking motion for both. You should see that in the original, the tail moves first, followed by the butt. But in reality, the tail should follow the hip wagging. I know, call me picky. But that's what being an animator is all about. It's the small stuff that'll make ya or break ya. Now, excuse me while I go back to staring at that swinging tail again for hours and hours and hours...murrrrrrrrr.

EDIT: I noticed that if you see a large, non-moving picture, click it to shrink it to the "small" size, and that usually kicks off the animation.

EDIT 2: My apologies to  taliesinthedragoon for not crediting him with the original design and animation of the avatar. At the time of my posting I really didn't know who did the first one. But I think he did a great job on it! It certainly captured my interest!