Diary vs Diarrhea

Conversation between me, R, and S one Saturday afternoon:

While getting all 4 kids situated in the mini-van and checking that R & S had their DS with them and plugged in I noticed S was hiding something.  (His DS close to his chest.)

Me:  S what are you hiding?
(S says nothing, but R chimes in.)
R:  It's a secret
Me:  What?
R:  A secret.  You know his diarrhea.
Me:  Diarrhea?  You mean diary.  I assuming they were using the chat/text function on their DS
R:  NO - Diarrhea.  His secret writtings.
S:  Yay - it's my Diarrhea
Me:  No R, you mean Diary.  Diarrhea is runny poop.
R & S:  Really?
Me:  Yes, Diary is a journal, secret writings, etc.  Diarrhea is runny poop that you can get sometimes with a tummy ache.
R & S:  Oh (as comprehension dawns)

Mind you I did this all without luaghing, but K was in the front seat laughing hysterically to himself.