When mice, attracted to the cheese of the moon (because, as we all know, the moon consists of cheese and cheese alone), travel to said moon and consume it to the point where the once all-cheese moon is entirely mice - as if to say, the moon is a sphere of mice and only mice such that when spaceships attempt landing on the moon, they cannot and instead travel through the center of the mouse moon and out the other side. During the journey through the center of the mouse moon, the spaceship only comes into contact with miles and miles and miles of mice.
Alex: When I traveled to the moon last summer, we found out that it's actually a Mouse Moon now.
Rebecca: Wtf is a Mouse Moon?
Alex: Dude, you know, when mice overtake the moon by eating all its cheese.
Rebecca: Are you stoned right now?