Drawing with both hands simultaneously is a pretty rare skill. Adolph von Menzel (1815-1905) could do it. His hands were cast in bronze holding a carpenter's pencil and a paintbrush.
H.W. Singer, in his 1910 book, The Drawings of Adolph Menzel said of him: "Menzel was naturally left-handed. When already past boyhood he trained himself to use his right hand too, and from that time could draw equally well with either. It is said that he continued making the rapid nature sketches with his left, and produced the careful finished drawings with his right hand."
(Video Link) This video shows a contemporary portrait artist drawing actors Morgan Freeman and Tim Robbins, with both hands going at the same time, and crossing over to help each other from time to time.
I find this performance impressive on many levels: not only using both hands at once, but splitting the attention to drawing two faces at once and drawing likenesses by starting with just an eye, apparently without a light structural lay-in to guide the construction.
This is far more impressive than my own relatively lame attempt at ambidextrous drawing.
Thanks, Christoph and Christian
Previously on GJ: