In Mirror, Mirror, when there is trouble with the transporter at the start of the episode, we hear this exchange:
SPOCK: Regrettable that this society has chosen suicide. Mister Kyle, you were instructed to compensate during the ion storm.
KYLE: But I tried, Mister Spock, I tried.
SPOCK: Carelessness with the equipment cannot be tolerated.
KYLE: But Mister Spock, I --
SPOCK: Your agonizer.
KYLE: No, Mister Spock.
SPOCK: Your agonizer, please.
And from there, he uses Kyle's agonizer to torture him. It's clear this is a normal consequence for not performing successfully in the mirror universe.
Has anything ever been written, or said, by Trek staff about why Spock would need to use Kyle's own agonizer? Why, as an officer, wouldn't Spock have one with him normally, to use on personnel who did not perform to his standards?
I am not interested in speculation. I know this may never have been addressed, but it's also possible that the author or someone else involved with production has elaborated on this.