In this scene the performers will be switched out if they evoke a laugh from the audience.
A No Laughs scene is not a serious scene. Learn Improv focuses on improv comedy, and the world of serious improv lies elsewhere. In a No Laughs scene performers are switched out when they get a laugh. This does not mean the scene is not funny. That happens often enough already.
The performers create a comedy scene with a narrative and characters. It may be a bit more subdued than a regular scene, but it need not be sad or overly serious. The performers will be playing things a little bit dead pan. If there actions evoke a giggle, guffaw, smirk, or snort from the audience the performer responsible for the fun is switched out of the scene. The host should call these switches and must pay close attention to the audience to do so.