Why does Connie go off with Arnold Friend

In Joyce Carol Oat's "Where Are You Going, Where Have You Been?," Arnold seems to have some kind of hypnotic control over Connie. It is not so much that he does something purposeful as if literally waving something shiny before her eyes, but the pull he has is almost palpable.
Her first impression of him at the restaurant includes his car:

...a convertible jalopy painted gold.

When he arrives at her house, the author describes Arnold's speech:

...he spoke in a fast bright monotone.

Arnold and his friend are both wearing sunglasses, but Arnold's glasses are noteworthy:

The driver's glasses were metallic and mirrored everything in miniature.

Like a child drawn to bright and shiny things, Arnold's car, glasses and even his speech seem to create a wave that Connie is unsuspectingly swept into.
There is more to this boy than Connie could imagine, and nothing for which she is prepared. A sense of something unnatural, even supernatural, is introduced—something beyond the natural world as she knows it. 

...the tiny metallic world in his glasses slowing down like gelatin hardening...

Talking to her as he rests against his car, he makes his "sign" in the air as if over her— that of an "X."

After his hand fell back to his side the X was still in the air, almost invisible.

Soon, a physical threat slowly comes to light. Arnold has already informed her that he knows where her family is and that she is home alone. Then he begins to lose the gloss, the shine:

"Maybe you better step out here," he said, and this last was in a different voice. It was a little flatter...

The more Connie looks at and listens to Arnold, the more upset she gets: dizzy and fearful. He seems to have appeared out of nowhere before coming up the drive; her vision blurs. His voice is lilting, almost like a chant.
When Connie refuses to come out and threatens to call the police, Arnold becomes more menacing. Eventually he says:

...if you don't come out we're gonna wait till your people come home and then they're all going to get it.

His message is clear.
When Arnold first arrives, Connie toys with the idea of being flattered or annoyed. For her, inexperienced as she is, it is a game. However, one can assume that as soon as Arnold first saw her at the drive-in restaurant her fate was sealed. The reader learns that he has been watching her since that night. By the time he arrives at her home, it's only a matter of time before she will leave with him. Like the spell a snake put its prey under, Arnold weaves his own spell. She realizes there is no escape for her. Her fear turns into emptiness and she listens as he gives her instructions. As she opens the door, it's almost as if she has an out-of-body experience (like someone who has died), watching herself move out into the sunlight and into Arnold's expectant and dreadful presence.