OK, we see he has just sneezed, and the force of it has left her hair blown back, and evidently left stuck in that shape. And what’s the joke? Is it just that?
I for a few moments entertained the idea that it was meant to be super-Eww and the stripe in her hair represented the discharge of his sneeze! But co-editor phsiiicidu kindly set me straight, that it’s just the standard Bride-of-Frankenstein stripe; and he provided this reference image: