On page 7 that isn't a smile... It looks like blood dripping from his mouth.

I think the scorpion guy looks kinda cool just from his expressions, he looks very evil and badass. But I'm not a fan of all the grotesque monster forms that we have been seeing lately. I like it to be ninja vs ninja, not alien vs predator.

Someone pointed out the links in his tail and looks very much like the links in the joints of Kankurou's puppets, so it is possible that Sasori could also be a puppeteer and the scorpion tale could be part of a puppet. I guess we will find out in 251 though.