Fibonacci Numbers

I was reading the Sunday papers and made a beeline for the comics section. 

My favourite comic strip is Foxtrot (Baby Blues comes a very very close second) and today's Foxtrot comic was sooo funny!

Let me upload it here ..

We've done trying to figure out why a riddle is funny.... so let me know why this comic strip is funny. (Yes it IS funny :p) In order to understand it better though, you'd need to know Fibonacci numbers.... and that's the only clue I'm giving you! 

Good luck fellow Math geeks!