I went on a photography walk with my dad the other day. In an alley, I saw an old clothesline pole which reminded me of my childhood. As a kid, my best friend's family and her grandparents both had outdoor clotheslines which look like metal telephone poles. Since I hadn't seen one in a while, I snapped a picture.
As I lowered the camera, my dad asked, "did you see the birds?"
Looking up, I saw two birds fly away from the clothesline.
When I got home, I zoomed in on the picture and found one bird peaking out of each crossbeam.
Writing can be similar to this process. Often I start a scene with an idea, get it down on paper, and in the process notice a nugget of something else. These two work together or be the start something else, but if I'm not writing or editing the muse will likely not peak out.