Split : Evolved Dr?

Did the Dr exhibit an evolutionary leap? How did she know about the trash? What about the handkerchief in the door jam?

Good question about the hankie in the door, maybe to keep it jammed so he couldn't lock her in there?

The doctor noticing how he reacted to the trash is probably just her being attune with average human mannerisms. Not to mention right before that people stepped around the trash but Dennis walked through it trying to seem normal despite being OCD.

As for the handkerchief, I think she was anticipating Dennis to become violent so she gave herself a way out should she need it.

I wish Fletcher had evolved (it would have been very fitting if she had telekinetic powers a la Carrie).
The observation re: the trash was to show what an astute psychiatrist she was.
The hanky bit shows that she read Nancy Drew and/or the Hardy Boys books when she was younger and had a keen sense of self-preservation. She suspected something was seriously off, and she knew she might need an escape route. Although that wouldn't have helped if the door had a deadbolt.