The side of the end of a hammer which isn't the side of the end of a hammer which you use to hammer a nail in, but in fact the side of the end of a hammer which you would use to pull a nail out.
I've just extracted a nail using my hammer's pleen.

He had just nailed his girlfriend's best friend - and there was no Pleen which could undo the work of that hammer (see shade).
by Shepherdess Tavern February 03, 2005
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