Sheldon Runs Some Tests

Being the little nut job that he is, Sheldon runs a few tests after Penny comes back from Nebraska with a cold.
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Sheldon and Leonard Sick

Sheldon and Leonard both sit together sick on the couch with no one to take care of them.
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Penny Takes Care of Sheldon

When Penny brings a cold back from Nebraska that she gives to Sheldon, she's stuck taking care of him when no one else will.
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The Big Bang Theory Season 1 Episode 11 Quotes

Sheldon: Anyway, the housekeeper in the faculty residence didn't speak any English. When I finaly managed to convince her I was sick, she said, "Möchtest du eine Darmspülung?"
Penny: What does that mean?
Sheldon: Based on what happened next, I assume it means, "Would you like an enema?"

If influenza was only contagious after symptoms appear, it would have died out thousands of years ago. Somewhere between tool using and cave painting, Homo habilis would have figured out to kill the guy with the runny nose

Sheldon