Hollow Unicorns

Richard Dawkins says:

[N]ot every English sentence beginning with the word “why” is a legitimate question. Why are unicorns hollow? Some questions simply do not deserve an answer.

Greg Knauss replies:

Why is a unicorn hollow? Since there is no such thing as a unicorn, it obviously cannot be filled with unicorn guts, because without unicorns there can be no unicorn guts. Therefore, it must be hollow.