The 15-45 second short scene before the opening song starts in a sitcom is called the “cold open.”
These short scenes set the mood for the rest of the episode. They often have no relation to the plot of the story, but are critical in drawing the audience in with a quick scene with as much humor as possible.
The best cold open is a scene that keeps the audience from switching channels.
First impressions are important. The first 15-45 seconds of an interaction sets the mood for the rest of the conversation. Make sure you have a strong cold open.
Blog of Jeff Wang 