Slivers of the moon

This evening, Clara saw the moon, and remarked that it was a full moon.

Tanja: It's not full, there's a sliver missing.

[2 minutes go by with some protests that it really is full]

Clara: The moon doesn't have a sliver. If it had a sliver, then the astronauts would get hurt when they go there.

Tanja: You're so funny!

Clara: You wouldn't think it was funny if you were an astronaut...