This is cool:
In her TED talk, she says all her arm muscles are already fully utilized, and that’s why she controls the thumb extension with her foot.
That’s not strictly true: many of us still have a vertigial muscle in our arms called the palmaris longus. That’s the muscle I’m trying (unsuccessfully so far) to have a surgeon externalize in one of my arm. It would be ideal to control this third thumb, as the palmaris longus is already a thumb abductor.