A couple of days ago Josh started a series of questions that lead us down this path...

Josh: "Mommy, what is a hiccup?"

Me: "Well, its a spasm in your diaphragm... (of course, followed by "what's a diaphragm?")
Its a muscle under your lungs- your lungs are organs in your chest that hold air when you take a deep breath-- take a deep breath....see how your chest moves?" etc. etc...

Several hours after our "biology lesson" I quizzed him.

"Josh, what's a diaphragmatic spasm?"

"I think its a very naughty dinosaur!"