"Mom. Mom. MOM. What you doing?"
"I'm changing the baby's diaper."
"Why, mom?"
"Because she pooped."
"Oh. [pause] Yellow poop?"
[struggling to answer as gravely as the question was asked, you know, out of courtesy] "Yes, son. Yellow poop."
"Not brown poop?"
[starting to lose the battle] "Um, no. Not brown poop."
"Oh. [another pause] I have brown poop, mom?"
"[AHEM] Yes. Yes, son, your poop is brown."
[And I should have seen it coming.] "Why, mom?"
"Just ... just because."