“It ain't always rocket science, sometimes a door is just a door.”
“Sometimes you just need to go through a door.”
“Getting a room's not always enough. Sometimes you gotta close the door.”
“Two U.S. Marine skeletons guarded the doors. They grinned down at us, rocket-propelled grenade launchers held across their chests."You know," Grover mumbled, "I bet Hades doesn't have trouble with door-to-door salesman.”
“Come on, Rory! It isn't rocket science, it's just quantum physics!-The Doctor (Matt Smith)”
“But just as the river is always at the door, so is the world always outside. And it is in the world that we have to live.”