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:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3232/
He was an EMT and it was about lifting someone in sync so they don't fall...
Pretty good joke, to be honest.
I think it's so the person being lifted doesn't tense, when ready for it. So you kind of surprised them but it's an acceptable surprise, as they are expecting a move.
These are usually either unconscious or screaming people, not the kind to care about what an EMT says.