First heard in Nickeloden's only good show, Invader Zim, in the episode "Dark Harvest". It controls all bodily functions. Getting hit in the Squeedily Spooch proves to be quite painful for any Irkin, as we discover, when Zim, the main character of the show, falls to the ground after receiving a blow from a dodge ball, clutching his midsection, where the Squeedily Spooch is located.
It's like a human male, receiving a kick to the testicular region.
Human: Arrrgh! My organs!
Zim: Whahahaha!! Inferior human organs!!!
Zim: Auugh!! My Squeedily Spooch!
-Zim and the little human boy, in the "Dark Harvest" episode.