In the car on the way to trumpet lessons:

Katie:  Mom, do stick shift cars even have a steering wheel?

Me:  (Laughing hysterically) Um yeeeesssssss!!!

(MORE and MORE LAUGHING!!!!!!!)

Katie:  Well, I hear kids talking about how hard it is to drive a stick shift so I thought that the car was controlled with just a joystick instead of a steering wheel.

(MORE UNCONTROLLABLE LAUGHTER!!!!!)

Katie:  So do they make certain cars in stick and non-stick?

I lost it. (Tears rolling down my cheeks.)

On the way home from the lesson I tried to explain to her what a stick shift was and then:
Katie:  So it controls the knees?
Me:  The what?
Katie:  it makes it go from one neeee to the other neeeeee?  (Think car sound effects)
That was it.  I almost had to pull over to avoid hitting something while I was driving.