The Hensel Twins
I just learned about these girls. They are dicephalic ("two heads") conjoined twins. They are amazing in how "normal" they are.
They each have a spine and a heart. They have three lungs, and share parts of the nervous system. Each girl controls her side of the body.
Their shared nervous system allows them to do coordinated activities, like play piano, type, run, etc.. But each does her own writing, take tests separately, do her own homework, etc..
They each plan on marrying, one each. Not to be nasty... but I wonder how that will work out? Also, what about pregnancy? Who will be the one pushing? Exactly which will be listed as the mother? There are some difficult situations coming up for them.
They were part of a special on The Learning Channel (TLC) on conjoined twins, which was taped when they were 11 years old. They just finished an updated special, entitled "Joined for Life: Abby and Brittany Turn 16", which will air January 17th 2007 on TLC. On the January 17th special, they will talk about how they will handle dating and other "teenager" realities.
More information: on Wikipedia, and a "fan-site".