Well, I already know the sombrero on the Mexican's back isn't a nice circular shape. Also, I hold my pencil weird and drag my hand along the page when I draw, so it smudges things... This picture wasn't meant to be some serious piece of art, so I didn't bother putting a blank sheet of paper under my hand to avoid smudging.

I think there's a problem with the Mexican's hips/thighs maybe, but I can't quite put my finger on it...