Why Are Blonde Jokes So Short?

So everyone else can remember them.

Two blondes were whooping it up down at the corner bar. One would shout "21 days!" and they'd laugh loudly. "21 days!" and the two blondes would high-five each other. "21 days!" Snortgigglegiggle "21 days!" clinking beer glasses together. "21 days!" while hugging each other all to the curious looks of the other patrons. Finally after awhile the barkeep comes over and says, "My, my, you ladies are having one grand celebration! I'll buy the next round if you'll tell me the significance of "21 days!"." The two blondes looked at each other and burst out laughing. "It's so amazing!" said one blonde. "Yes!" said the other, "We bought a jig-saw puzzle and we put it together in 21 days!" The barkeep looks at the grinning blondes and says "...So?" The blondes see his questioning look. One blonde says, "Silly... it said right on the box...3 to 4 years!"