12 characteristics of film noir

I recently joined the social-media Q&A site, Quora.
This adds to my list of sites where I am a member but I don't really know what the site is all about.
It's like I am in the middle of a film noir and I know I will leave the cinema without having figured it out. Luckily Film Noir is one of the topics they ask questions on and that is a topic I do know lots about. Here is one of my answers:

Let's try to create a list of 12 characteristics starting with features common to all/ most film noirs. 
1. Films Noir are almost  always crime films. 

Out of the Past
2. Shadows are essential to noir. The shadows mirror the mystery and maintain the suspense.

3. Sharp dialogue is important. The caliber of the writer determines how clever the quips are but even the best writers like to introduce some strange lines. The femme fatale in The Big Sleep says at one point. "Ï should throw a Buick at you." This is the scene where she says she does not like Malowe's manners. He replies:. "I don't mind if you don't like my manners, I don't like them myself. They are pretty bad. I grieve over them on long winter evenings."

Detour

4. Unusual camera angles. They might shoot up or from the side  or deep focus to unsettle the viewer, again to create suspense and deepen mystery. The feeling is of pending doom.

The Asphalt Jungle

5. Light penetrating the darkness. An old favorite. Shine a torch into the face of a leering villain or a distressed anti-hero and you have a powerful image.
6. Low budget or an appearance of low budget in telling a bleak tale.

7. Horizontal or vertical bars across a scene. I am not sure whether the image is of prison or peeking through a venetian blind, but you will see this type of image a few times during nearly every noir.
8. A tragic ending. It does not always end tragically but it usually does and even the ones with a relatively happy ending never seem to be heading that way. We are relieved when the anti-hero is allowed to return to a normal life of quiet desperation.
9. Corruption. Crooked cops, politicians, doctors and authority figures abound in noir. The cynical might say they abound in real life, too.

10. Private detectives (or unofficial detectives)  and femmes fatale are only in a minority of film noir but some noir buffs such as me love them. When I wrote my neo-noir novel Iraqi Icicle, I made sure I had an unofficial detective and a femme fatale.

Detour: Flashback coming on.

11 Flashbacks. It is a great way to resolve the mystery introduced at the start.

The Maltese Falcon
12. Sinister urbane villains. The sophisticated villain of the modern action film was born in film noir.

Have you any more? I know cigarettes are a trope but smoking was prevalent in a lot of films in the 1940s and 50s.