Nothing.

Am from critique group. Pretty sweet idea for a piece, you made the crows coming out of his mouth look pree good. I ain't about to critique the head because I'm not very good at them myself. One thing I can say though is that you should push your values more. The lightest value of the head is too similar to the paper so it just blends. It looks cool how it's pretty transparent though, but in that case just lighten up the bits closer to the crows.