Offscreen - it's filmed in a way that you don't really see any of the smacks landing.
This is a scene that is meant to be funny, but exemplifies some common problems for kinksters in a vanilla relationship.
The girl is not ready or willing to come out to her boyfriend about her needs (which is sad and a guarantee for a later break up or unhappiness ). The boyfriend learns about her kink, but doesn't talk to her either.
And not being informed or understanding what this kink is all about he completely fails in setting up and executing the spanking. Of course it will be hard for any partner not into spanking to be up to the task. But this approach will of course fail anytime....
