Here are some answers from the third-year immunology exam. They are all sadly genuine.
Viruses are constantly changing their surface antigens by continental drift.
The sympathetic division (of the ANS) is involved mainly in physical activity and the parasympathetic is involved more in vegetation.
Antibody coats antigen like coconut on a lamington.*
*For those unfamiliar with lamingtons, they are cubes of sponge cake, which are coated with a thin layer of chocolate and then sprinkled with coconut.
[Thanks to Sue for these little ... um ... gems. I'm so glad I didn't have any marking to do this semester!]