xkcd #3232: Countdown Standard
Title text:
Anyone who is caught counting ‘three … two … one … zero … GO!’ will be punished with a lifetime of eating only ISO standard food samples.
Transcript:
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Source: https://xkcd.com/3232/
Apollo 11 voice goes ‘4, 3, 2, 1, 0, liftoff’.
Liftoff is a non-integral byproduct of the countdown, not an actual canon part of the sequence.
If you don’t say liftoff then the rockets don’t ignite.