The ending

I thought he was dead and she was imagining him being alive. That's why he had those zombie eyes. 7/10

Look at the night sky, where does it end?

I think it was to either

1. Make us viewers think that it is her cheating boyfriend (who had the same haircolor) in the cage initially

2. A way to get her frustration out on her cheating boyfriend by seeing him torture himself pretending he is him

Or both

I got keys coming from overseas! T.I.P. Syke

That's exactly right! The ultimate sadist/masochist relationship.

"It's as much fun to scare as to be scared" -- Vincent Price

I dunno. She pretty clearly cut this throat. And in the cage at the end he had no scar there.

I think she imagined the entire set-up from shortly after he showed up at the diner. She stalked and captured him... but in her "story" she was the one captured.

None of what we saw really happened. Just like she never talked to Claire. We can assume she is mad and did really think it all was real or that she just wrote the captive\cage story for her now to be published book; all the while keeping Seth as a living inspiration. Either way she never spent a day in that basement cage and the black security guard is alive and well.

No doubt she is a killer. But rather than kill Seth she made him a pet. A mascot. She probably had real feelings for him and that motivated the capture.

Seth vanished and never returned to his job at the kennel. Again, that entire story line was in her imagination.

This^