Mysterious nomenclature

["Psychos 'R Us" <honge@creighton.edu>]

I know the existance of S1, S2, and S4 (now S6). But what is a S5??

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Looking for roadkills... drop it by honge@creighton.edu...
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Q. What did Tarzan say when he saw the elephants coming over
   the hill towards him, wearing sunglasses?
A. Nothing... he didn't recognise them.
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