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noun. In the flash animated series of Homestar Runner cartoons, a non-existant wonder that Strong Bad uses by looking into a paper bag. Homestar Runner has hopes that he will someday be allowed to see the Thing In A Bag, and does errands for Strong Bad to curry his favor.
HS: What are you doing?

SB: Hanging out at The Stick, looking at a thing in a bag.

HS: Can I see?

SB: No. It's for me. And The Cheat. And Strong Mad.
by Marc February 24, 2004
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