The Scream Extractor is, as the name implies, a scream extracting machine which has the intent of collecting screams much better than even scarers. It has 15 Scream Canisters. Randall Boggs was going to kidnap Boo to test it and see if it will collect screams exactly as he expected it to, then work with Waternoose to kidnap hundreds of children to extract their screams in order to stop the energy crisis in Monstropolis and bring Monsters Inc. back on top. It's demonstrated that it extracts the victim's breath along with their screams, which can potentially suffocate the victims, even monsters.
The Scream Extractor first appears when Randall thought he captured Boo, but discovered that he had Mike Wazowski instead. Despite this, Randall decides to test the machine on Mike to make him expose Boo's whereabouts. Luckily, Sulley is able to unplug the Scream Extractor's plug before it can suck any screams from Mike. Whilst Randall goes to put the plug back in, Sulley frees Mike and replaces him with Randall's assistant Fungus. When Randall returns, he finds the machine sucking screams out of Fungus. After switching off the machine, Randall asks Fungus where Mike is, to which Fungus (who is too weak to talk) points to the direction he, Sulley and Boo went.
The machine later reappears when Randall prepares to use it on Boo, whilst Mr. Waternoose watches on begrudgingly (after he banished Sulley and Mike to the human world). Luckily, Sulley returns from the human world and pushes the Scream Extractor away from Boo, before ripping the horrific device from its circuits and he tosses it at Randall and Waternoose, pinning them to the wall, before fleeing with Boo.
In Monsters At Work, it is revealed that the Snowman was banished because he read the letter contains the blueprint of the machine.