"The liver pâté demands that the polar bear leaves the room."
Translation:Leverpostejen kræver at isbjørnen forlader værelset.
One is to (deliberately) leave an area, the other is to (often accidentally) leave an item/a person/something behind. To "forlade" your wife and kids means you walk away from home and don't come back, to "efterlade" would mean you leave them at the station or something.
It's pretty simple actually. Basically you have two sentences connected with "that/at", "The liver pate demands" being the main clause and "The polar bear leaves the room" being a subordinate clause. Now you go on and translate both clauses and stick them together with "at".