I've said it before, AChat takes full advantage of the fact that the avatars don't have the skeletal/musculature system people do.
The crab is a perfect example, but now that I've had the chance to try it I have to say I REALLY like it. I LOVE that I can have sex on here that I would have to limber up for in real life with zero fear of falling and hurting myself.
Add to that the amazing graphics and you have another win for the development team.