不会骑马的骑士

A:   I am a pigeon expert.   I can tell the male pigeons from the female.
B:   How?
A:   That's simple. The male pigeons always eat female worms and the female pigeons always eat male worms.
B:   Now, how can you tell male worms from female worms?
A:   I need not answer that. I'm only an expert on pigeons.

[譯註]  
A:
我是鴿子專家。我能分辨雄鴿和雌鴿。
B:
怎麼分辨？
A:
那很簡單。雄鴿總是吃母的蟲，而雌鴿總是吃公的蟲。
B:
那麼，你怎麼分辨公的蟲和母的蟲？
A:
我不需回答那問題。我只是鴿子的專家。

　
註：pseudo-expert (假專家)， pigeon =   dove (鴿子)， tell A from B (分辨 A 和 B)。