Why didn't Dennis see Casey when he entered the car?

When Dennis enters the car in order to abduct the girls in Split, he sprays the two on the back seat but completely ignores Casey, who sits right next to him on the passenger seat. Only after she tries to open the passenger door and makes a sound does he realize that she is there and goes on spraying her too. Can't really explain why.

I have two possible hypotheses but none of them are satisfactory since none comes with solid proof.

He doesn't perceive her because she is not "unclean".
His brain does not perceive her because he was expecting only the two other girls (whom he stalked for 3 days) to be in the car.

If anyone has a clue, I'd really like to hear about it.

plot-explanation split

Best Answer

He does see her, but simply ignores her. She's not reacting the same as the girls in back, who immediately confront him. She simply sits there, not moving and not saying anything.

She doesn't give him a reason to spray her until she makes the move to open the door.