The counting sheep are shown to be desperate for work in wanting people to sleep at night, but get frustrated whenever they found out people have a Serta mattress.
This humorous scenario highlights the sheep's reliance on humans sleeping and their frustration when faced with an obstacle that disrupts this expectation. The mention of a Serta mattress adds a layer of humor by suggesting a specific brand associated with comfort, which contrasts with the sheep's desire for people to sleep.