You’ve seen this video previously, but watch it again and focus only on how Kristina delivers the reinforcer.

She uses the reinforcer to get a bit more of the behavior. This can be a good strategy, but it can also backfire if you ask for too much extra effort in order to get the reinforcer. He’s already earned it, so he shouldn’t have to work too hard to get it. This is where trust and knowing your learner come in to play. Kristina has a very trusting relationship with Mik and she knows how much extra she can ask for to move the behavior further along. If you try this and it causes frustration, then immediately on the next turn be sure that the learner gets the reinforcer without additional effort.