Thank you very much for the A2A!
In songs like Killer Queen and Don’t Stop Me Now, Freddie employed a high mixed voice regularly. That phrase in Killer Queen switches from an upper mixed chest voice to a head voice/falsetto on “well versed in etiquette,” then back to chest voice and full voice on “extraordinary and precise,” and then into the chorus: “she’s a killer, Queen, gunpowder gélatine, dynamite with a laser beam, guaranteed to blow your mind.”
If you have the range to match your phrase, that’s fantastic! It’s a difficult shift that many professionals have trouble with. Because of Freddie’s tremendous vocal range and power, Queen’s songs is notoriously difficult to sing.
This isn’t my area of expertise, but I believe he sings it in his brain. There is a considerable difference between head and chest voice for most vocalists, especially males. On the final syllable of the first stanza, “de-cline,” he switches from chest to head voice. Then he continues in his own voice in his brain.