Removing the error tag - his hand does look odd, but that really -is- pretty much the way a hand looks when flexed back that far.
I'm also tempted to change the rating of this down to rating:q, since the focus is on the act and not the anatomy. However, even though there's nothing actually visible, I think there's a little too much bodily fluid showing to warrant anything less than rating:e. A few drops that might pass as sweat might be ok, but this is quite a bit beyond that.