We all know that a lot of the face, mouth and throat are involved in producing sound, but it takes a video like this to demonstrate just how complex our vocalisations are. In it, you see baritone Michael Volle singing "O du, mein holder Abendstern (O Thou, My Evening Star So Sweet)" from the opera "Tannhäuser" by Richard Wagner, as viewed using high-resolution magnetic resonance imaging.
It's not just for the coolness of it. Volle was taking part in a study conducted by Matthias Echternach and colleagues at the University Medical Center Freiberg's Institute for Musicians' Medicine in Germany to examine how the vocal tract changes while singing. Echternach, himself a former boy soprano and tenor, has been using MRI to study singing since at least 2008. Here's another video.
And if you want to see what Volle looks like singing from outside his head, you can see a video here.