Refers to the large void situated in the main room of "Temple", the infamous multiplayer map for Nintendo 64's Goldeneye. Until the release of Perfect Dark, things would only travel out from the sphincter (eg. bullets, remote mines). The long awaited Perfect Dark allowed players to jump into or "enter" the Sphincter, creating a 2-way traffic system which revolutionized the tactical approach when fighting for the Temple.
Eric - "Shit, I saw the fuckers, they're down the Sphincter"

Jim - "Throw a timed mine!"

Eric - "Timed mines are shit! Who the fuck uses them anyway?! I'm going in..."

Jim - "You cant enter the Sphincter of Doom here! You're thinking of Perfect Dark!"

Eric - "Shit, fuck, I knew it, now I've lost them. Why is there a fucking invisible wall anyway? Why would i NOT be able to jump down?"

Jim - "Chill man, meet me at the crossroads We'll get 'em there"
by Nickeatworld March 1, 2009
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