Nightmare Fuel / United 93

• United 175 hitting the South Tower, which is shown through archive footage. While none of the passengers are shown, one of them was 2 year-old Christine Hanson, the youngest victim of the attacks.
• The stark realism of United 93 being hijacked definitely counts as this — the panic, terror at seeing a fellow passenger stabbed, being forced into the back by a man wearing a fake bomb... Everything.
• The entire ending. The passengers do break into the cockpit, and one guy tries to force the plane up while fighting the pilot... But then we get a view of the window, as the ground gets closer and closer. And then, a Smash to Black before the plane hits. John Powell's score makes this hit harder.