whilst we are on silly jokes.... why did the ostrich stick his head in the ground.... because he farted....
AND... why did the egg cross the road? because it was a chuckie egg.... (this one from my 2 1/2 year old niece).
RHere it is, they reckon it could be down to climate change http://www.iht.com/articles/2006/03/08/healthscience/snrain.php