Some things I can say and some things I can't

It occurred to me.

That was when I was an elementary school student.
I was eating school lunch with members of a group.
We talked about butterflies.

Then I said that the eggs of a cabbage butterfly resemble rice.

When the whole scene suddenly changed.
That day's lunch was race.
No one spoke a word to me.

I think this joke was difficult for elementary school students.