Learning Not to Be Surprised

So today my son was drawing with his Magna Doodle:

Son: "Look, Mommy -- it's a house with rain coming down!"

Me: "Wow, that's great, sweetie!"

Son: (erasing and drawing something else) "Now it's a picture of me!"

Me: "Wow, that's really cute!"

Son: (erasing and drawing again, then looking at me for a moment)

Me: "What's that, sweetie?"

Son: (grinning) "It's a giant PENIS!"

Me: "Um...wow! So...what made you decide to draw a penis?"

Son: (nonchalantly) "Oh, I just thought it would be fun. Look! I'm drawing a car now!"

Me: (heading to kitchen for Tylenol) "That's really great, sweetie..."