This is so fascinating to watch. See how his tongue swells as he hits the “E” vowels. The amount of space open in his mouth is tiny, yet the sound is tremendous. Interesting fact about opera singers: when they sing at full volume they are moving such a small amount of air over their vocal chords that if you held a candle in front of their mouths, it would barely waver.
Having studied opera for 5 years at CUA, your contributor can tell you that this video would have been invaluable for learning the tongue positions to maximize the power of your head voice.