Well, first video and first music stop :
Musical Chairs at SWVA Gaming for an Antec HCP-750 Power Supply - YouTube
The guy who jumps that has no sleeves jumps two to three times after music stops.
Those are three easy strokes after a "stop"
Keep in mind he was WAITING for the music to stop, with NO DISTRACTION for that action.
Having a single specific response to a single specific stimuli is one of the simplests forms of reaction.
In sex, you have the distraction of your own pleasure ( which will always slow your reation time) you are NOT waiting for the person to say "stop" at any moment and while you do are paying attention to your partner, you will comply to commands which are unexpected, this means that s/he will have to make choices and react differently to a lot of otherossible commands like "hit harder" "go slower" " go faster" " keep doing it" "yeah baby" " right there" "to the left" "did you lock the door?" etc.
Now, the reaction was still be fast, those were one or two seconds, but it was three jumps, to a much simpler reaction test that what can happen mid sex.