Hoist with one's own petard

[len_leeb@domain.elided]

My Webster's says that the correct spelling, the Bard notwithstanding, is 
"PETARD."
The definition of the phrase is "destroyed by the very devices with which one 
meant to destroy others. Hamlet, III, iv."
So, Will S did use the phrase, and John H's copy of Shakespeare may have a typo.
The definitions of the word petard are interesting, too:
To break wind
A metal cone filled with explosives, fastened in ancient warfare to walls and 
gates and exploded to force an opening
A kind of firecracker

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