A Spider Theory

What is scary about a spider?
What is the first thing you notice about a person when they enter the room?

I was once asking my Metro vendor about his regulars.
He explained that he recognizes them by the way they walk.
(He also explained that he knows when somebody wants a paper because they raise their eyebrows. I might write a little on body language anon.)
A fellow lecturer and I were discussing something similar, and she suggested that the first thing she notices about a person is how they carry themself - how they enter the room.
I've heard many women say something similar - about, perhaps, meeting a man for the first time and forming an instant impression from his posture or movement - the way he carries himself. Does he slouch or walk tall? Does he move quickly or slowly? Does he swing his arms or have his hands in his pockets? Add to this subtle gestures and expressions, and you can (and will) create quite an impression of someone in the blink of an eye without knowing a thing about this person.
Consider the effects of these alternative intros:
He waltzed into the room;
He snuck into the room;
He shuffled into the room.

And spiders. One of the things they have in common with other scary beasties - snakes and, my own phobia, giant centipedes - is their apparently aggressive and unpredictable movement. Spiders have eight legs and scuttle. They are remorseless and quick too. They come at you. And you can never be sure which direction they are going to veer off in next.

Movement is a powerful tool for the writer.
The movie Silent Hill demonstrates this technique well. The demons might appear to have oddly-jointed legs, and stride or swagger in a most unnatural manner, or they might scurry across the flagstones on tiny, fat legs. Some move slowly and some move at speed, but they always move towards the protagonist and always appear unstoppable.
A thesaurus helps us to find the mot juste - the perfect word for the perfect movement.

Kate Grenville uses movement to convey the differences between the British settlers and the 'blacks' (and, indeed, isolates the settlers by distancing them from the movements of nature too, whilst bonding the 'blacks' to nature using foreign movements [along with a control over nature that the settlers lack]). Check out all the movements in this passage:

'She bent and picked up a lizard that struggled in her hand. With an unhurried movement she shook it and it hung limp. As she tucked it into the string around her hips, she called out high and shrill to Saucy Polly, and Thornhill could see Polly's white laughing mouth as she called back and flicked her hand toward the lizard. Even the way they gestured was different. Their hands were so fluid it seemed that they had extra joints in their fingers, and a wrist that was constructed in some other way altogether, along the lines of rope rather than bone and sinew.'