Many of us have complained over the years about the dearth of facial expressions for human avatars in Second Life. The avatar skeleton has no facial bones, and facial expressions have been limited to the dozen or so stock "facial morphs," most of which look pretty creepy.
And those of us with non-human avatars have had to crush our bodies up small and hide them inside body attachments, which were often animated with a very complex and often clunky special HUD.
But Linden Lab has just announced the trial release of "Project Bento" which aims to solve both problems by adding a number of "bones" to the avatar skeleton. The new features are now available for experimentation and comment.
Note that (unfortunately) LL has not changed any of the existing skeleton structure. Much as I would like to see more realistic movement of, say, the shoulders, I am forced to agree that this was a good decision on their part. Changing existing bones would break all kinds of content...pretty much any existing animations, and clothing and attachments that depend on those bones for their movement or deformation.
Read all about Project Bento here: https://community.secondlife.com/t5/Featured-News/Introducing-Project-Bento-New-Bones-Added-to-Second-Life-Avatar/ba-p/2987206