The proximal phalanx of the thumb really does not hyperextend backwards like that, though. Especially not when the thumb is also bent at an acute angle at the same time. ^_^'

These muscle fibers.... whoa

Here's my attempt. It doesn't feel done, but I feel like moving on for now. The gesture and face feel a bit off, as does the shading. I started out doing the blender stick smudging technique, but then watched the videos through and attempted the rest with the crosshatching technique Proko recommends. It was a great challenge, and I learned a lot! Thoughts and critiques welcome!

Good stuff - critiques welcome