The one time playing as a sub I had to safeword out of a scene, I was not capable of saying the safeword. I wasn’t gagged (in which case it would have been tapping out anyway), but I’d gotten into a psychological space where it was not emotionally possible for me to speak. To get out of it, I had to struggle out of submission and onto solid ground from which I could explain that I was not OK. So instead of gasping, “Red,” I said, clearly and quietly, “We’re going to have to stop now.” My Dom listened, and we worked through the difficulty.
Because the safeword was emotionally linked to submission, saying it would have thrown me right back into that quicksand. Being unable to speak the safeword isn’t unique to me; over the past couple of decades, I’ve seen it happen a number of times. Only once or twice with my own submissives, since I generally don’t rely on safewords. Which isn’t to say I don’t use them at all. I just don’t expect that they will work, and I certainly don’t imagine that my responsibility as a Domme starts with hearing the safeword.