 Correctis effects. This is the learning that happens when you don't want a little to learn, right? This is learning that occurs when you don't have control over it. This is learning occurs that because they're just practicing the baby, they're performing the response and then they get better at it just because they're performing it because naturalistic reinforcers and yeah. Anyway it sounds like it's a good thing right? No, because it makes you look like a fool. Practice effects prevents you from drawing conclusions about the effect of your independent variable because you don't know if your independent variable had an effect or who's the practice? Oopsie. And so oftentimes we want to tell you, stop learning! I did not give you permission to learn that independent variable in place and once I put the independent variable in place you can then learn, right? So we have to watch out for practice effects in an experiment especially multiple conditions because people might learn from what they're doing. Assessments are an issue. You do all sorts of assessments where you don't want to put them back to back or you want a good amount of time to find a good amount of time. Between assessments that way whatever is being assessed is not having a practice effect on the second measure. All sorts of things with practice effects. They're kind of tough to tease out to design your experiments. Well please, thank you.