Explaining the joke

(scene opens in messy kitchen)
Alpha: Mom, I don’t understand why this joke is funny.
Me: What’s the joke.
Alpha: It says Captain Kirk has three ears: left, right, and frontier. What’s a frontier?
Me: (with immense sonorous gravitas) Space, the final frontier. These are the voyages of the Starship Enterprise. Her five-year mission: to explore strange new worlds, to seek out new life and new civilizations. To boldly go where no man has gone before.
Alpha: (silence)
Me: (goes back to washing dishes)
Alpha: Wow. I’m going to have to start watching Star Trek.
Me: Indeed.