The Giraffe Joke

At this point, I was teaching a girl of 7.  Her 5-yr-old sister was always in the lesson as well (very well-behaved).  Neither girl was particularly tall - the younger one was about as tall as my navel.  At the end of this lesson, the little one gave me a hug (fairly standard procedure), and, still with her arms wrapped around me, looked up.

Girl: Miss Anna, do you know why giraffes have such long necks?
Me [smiling at the irony]: No... why do giraffes have such long necks?
Girl [starting to giggle]: Because... because they have smelly feet!!!