This is an excellent image. However, how do we know that it's a night shot?

I really like this. At first I was not quite sure why this would be categorized as a night photo, so I let my imagination kick in and picture this as a mousetrap illuminated by the glow of the moon, sitting in some quiet, lonely, remote corner of your house waiting for its prey. Cool.

this is very clever!

Great take on the theme

I don;t know. This isn't clearly a night photogrpah, although I could beleive it was taken at night. But IMHO it is just a very cool photograph of a common object, so I had to give it high marks on everything except relevance. I really like the bluish color cast.