 That's another one of our acronyms. Not mine, not Brad's, not someone else's. It's just an acronym out there. I blame Mechner. Look up our video on Mechner notation. So anyway, S plus. It's an SD before it's an SD. Sorry, folks. It really is. It's a discriminative stimulus. It hasn't become a discriminative stimulus yet, but you're training it to be one. So in here, when Brad and I first started doing videos ages ago, the camera was maybe in S plus. We were trying to make it in S plus. We were using it as an S plus. So it becomes a discriminative stimulus to do effective communication about behavior analysis. So I think it has become that. But when it first started, it was a little bitty stimulus. It was just an S plus. And then when it grows up, it becomes an SD. So through reinforcement in the context of that SD and not in the context of other stimuli, an S plus will become an SD. So as my child is making noises in the background, don't really care. It's all good. So again, we have S pluses become SDs over time.