Dumbledore was humming quietly, apparently quite at his ease, but the atmosphere was thicker than cold custard, and Harry did not dare look at the Dursleys as he said, " Professor—I'm ready now."
He ran until he was out of breath, and then, becoming more courageous, walked leisurely along, singing in an old voice a little song about a sailor-boy and a fair one, and bright gold in store.
From there, the facial nerve branches off to different facial muscles that help with facial expression, like the ones you use while whistling to your favorite song.