Prose writers tend to write horizontally from left to right. Screenwriters write vertically down the page, which creates a dynamic pace that speeds up the reading:
LAMBERT
What's the matter.
KANE
I don't know... I'm getting cramps.
The others stare at him in alarm.
Suddenly he makes a loud groaning noise.
Clutches the edge of the table with his hands.
Knuckles whitening.
ASH
Breathe deeply.
Kane screams.
KANE
Oh God, it hurts so bad.
It hurts. It hurts.
(stands up)
Ooooooh.
BRETT
What is it. What hurts.
Kane's face screws into a mask of agony.
He falls back into his chair.
KANE
Ohmygooaaaahh.
A red stain.
Then a smear of blood blossoms on his chest.
The fabric of his shirt is ripped apart.
A small head the size of a man's fist pushes out.
The crew shouts in panic.
Leap back from the table.
The cat spits, bolts away.
The tiny head lunges forward.
Comes spurting out of Kane's chest trailing a thick body.
Splatters fluids and blood in its wake.
Lands in the middle of the dishes and food.
Wriggles away while the crew scatters.
Then the Alien being disappears from sight.
Kane lies slumped in his chair.
Very dead.
A huge hole in his chest.
The dishes are scattered.
Food covered with blood.