 Arbitrary stimulus class is basically any antecedent stimulus that elicits or evokes or whatever you want to say depending on your operant or respondent, but whatever. We'll think of this in an operant setting. It's always easier. Evokes the same response, right? So for example, the example that we like to use is like food, all sorts of stuff. I mean, food, right? This could be food. No people eat these and I'm not going to explain why. This is kind of food, but we'll say it's food. Anyway, the idea is that the stimuli don't resemble each other in any way, but they evoke the same response. It has to do with response generalization and a whole bunch of other things, or stimulus generalization and a whole bunch of other things. But the basic point is that their stimuli, they're not really related. They're not related in space and time. They're not related in physical form shape. They're not related in location and all that stuff. So they're just really unrelated stimuli, yet they evoke the same response. And that's the idea. That's why they're arbitrary stimulus class. So, I go. I'll show you.