1) I don't know how many vocal tracks we're actually listening to (I suspect at least 4), but notice how many other instruments are shared on those tracks - claps, finger snaps, piano and horn.
A bit of history - in the days of multitrack magnetic tape machines, we'd run out of tracks pretty quickly since there were a limited number available (this song was probably done on a 16 track recorder), so the only way to add more instruments was to find a blank space on one of the tracks and record it there. That took a lot of skill to make sure you recorded the part without erasing a bit of the one previously recorded, and it also made for very interesting mixing, since they became complex very quickly when you had 3 or 4 instruments or vocals occupying the same track.
2) Freddie Mercury's vocal mic is a bit distorted at the beginning of the song, which makes me think that this was a one take affair since it cleans up as the song goes along. It might even be that both singers sang into the same mic, since Bowie sounds great but the mic sound isn't very flattering to Freddie. Ken Scott, who produced 4 Bowie albums, once told me that all of David's vocals that he worked on were always done on the first take. If this vocal track was a first take recording, the vocal performance for both singers is great.
3) Check out how the reverb is muted at 2:05, then reappears with a lot more intensity at 2:20. Also, the claps and finger snaps have some reverb at the beginning of the song but not the ending.
Have a listen.
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