thin red line (TM)

This is the last post for this week, just a simple one, but the idea about the line is interesting. I use Curve and Level tool to make the background black.(Honestly, the background , which is the wall when I captured the image, is dirty so I cleaned it .I intended to do with some environment , but I don't find one). Again using some old tricks like filter tools to emphasis the line, and then change the color of the line.
What a weird one.