This is not really a joke. It may infact be completely true. Who knows?

Windshield testing
------------------

Scientists at NASA built a gun specifically to launch dead chickens at the
windshields of airliners, military jets and the space shuttle, all traveling
at maximum velocity. The idea is to simulate the frequent incidents of
collisions with airborne fowl to test the strength of the windshields.

British aircraft engineers borrowed this technology to test their own
aircraft windshields and found that the windshields cracked on impact with 
the dead chicken.

The horrified brits sent NASA the disastrous results of the
experiment, along with the designs of the windshield and begged the
US scientists for suggestions.

NASA responded with a one-line memo:

        "Defrost the chicken."