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Nightmare Fuel: The War Of The Worlds
The scene where the aliens first show their hostility - by deliberately, systematically exterminating a crowd of unarmed civilians with a heat ray and destroying every structure in front of them with their Wave Motion Gun. Human bodies turn to nothing but ash, leaving their clothes flapping in the wind. A bridge full of stopped traffic fares little better. Put yourself in Ray's place - he's running for his life, while people all around him are being incinerated. The only reason he survived that attack is Plot Armor. No mystery why he arrives home an ash-covered, shell-shocked wreck.
The Ferry scene, where we're introduced to the all-new terror of the Gatherer Tripods. Ray and family just barely survive the horrors of the sinking ferry and swim clear, only to get a front row view of the two choices humanity is given: be vaporized or be harvested. All to mingled screams of an air raid siren (from the town) and the ferry victims being gathered by the Tripods.
The general chaos of the refugees turning against each other.
The flaming train scene with Rachel at the river, where we see bodies upon bodies slowly floating..
What makes it even scarier is just beforehand Rachel says 'Looks like the power's still on here.' Imagine what would've happened if it wasn't and the train crossing bars didn't go down.
Ray killing Ogilvy. First he covers Rachel's eyes with a blindfold, telling her to sing her favorite lullaby to herself. As she starts to sing, he takes her hands and covers her ears with them... then walks into the other room and the door falls closed. We don't have to see what he does in there- we just know that Ogilvy is dead.
The scene where Ray and Rachel are finally captured by a Gatherer Tripod, and and put into a holding cage with a bunch of other people sobbing and screaming.
It gets worse when the Gatherer Tripod reveals why it was capturing people: to be 'fed alive'' to it, one at a time, both to feed the organic portion of the Tripod and make fertilizer for the Red Weed.