I can most often easily trace where dream images/events come from, and if it doesn't seem really obvious to me then a little bit of thinking back generally lets me figure it out.
I don't know about other people's dreams, but my own aren't at all mysterious. They're usually pretty much a matter of "the week in review", with any number of things that had some (even minor) impact on my thoughts when I ran into them. Then, though, it's like all those recent "thought-impacting" things get all mixed up and come out as the images to whatever story is in the dream. Sometimes the story in the dream (or whatever version of "story" any dream has) is also something that was (sometimes) a fleeting concern or thought that occurred to me recently. Once in awhile, though, I can tell that the story is more about things that have bothered me in my life on a more long-term basis.
Here's the kind of thing it might be if I were the one who had the leopard/window dream: Maybe I'd seen a cologne add with a leopard in it (online). Maybe I didn't think I thought anything about it. Then, maybe, I talked to the cat next door a few days ago and noticed that he moves like a bigger cat (and maybe I didn't even really think about it).
Then, maybe, I had been thinking about opening my windows for Spring, which would make me recall hearing coyotes last Fall and make my mind briefly go to the idea that there are wild animals that come through the yard. (Actually, after seeing a coyote in my yard for the first time I did wonder if, when my daughter's cat sat in the screened window, a coyote may want to get to the cat badly enough to try jumping in through the screen).
So anyway, if I had that kind of leopard/window dream it would mostly likely come from that kind of "collection" of images/thoughts that had (even briefly) had some impact on my thoughts over the course of recent days.
For me, things I've seen and noted, comments I've made or others have made, fleeting thoughts that have occurred to (or worried) me, images or words I've seen online or on television. Maybe it's even some little thing I noticed that made me temporarily think of something else after being reminded of it.
I know there are people who would disagree with me about dream images/stories not meaning more, or meaning something universal, for everyone; but, boy, I know my own dreams and how/why things make their way into them. Maybe everyone's different, but I'd bet the leopard dream could be tracked. :)