Experienced this recently, twice. I read a retelling of The Fall of the House of Usher (book is What Moves the Dead by T. Kingfisher) a couple weeks ago. After that I read my next book, The Fisherman by John Langan, and they had similar vibes, though completely different overall, but they both had supernatural elements and dealing with losing loved ones. And i thought there was an interesting similarity between the two. I don't want to give too much away, because they're both great books and I don't want to spoil anything.

Another time, happened a couple days ago. I'm currently reading two books: The Hollow Places by T. Kingfisher; and What-the-Dickens by Gregory Maguire. I had just gotten to a part in What-the-Dickens about a being (fairy thing of some sort) finding themselves in a tin can, and it's attacked by a cat, its a whole thing.. Then when I went to read my other book later that day tin cans were also mentioned. It was just random, but I thought it funny that in two totally unrelated stories, read on the same day, each would feature a bit about tin cans.