Overheard

at Botanic Gardens last Saturday

Papa: Matthew, 月亮在哪里?
Matthew: 在那里.(pointing to the moon in the night sky)
Papa: Matthew, 半个月亮是 half moon.
Matthew: 爸爸, 两个half moon 是什么?
Papa: eeerrrrr... (obviously stunned)

after a while, it suddenly struck Mike... 两个half moon 是 full moon!