If something goes wrong in a scene and stays in because it adds some reality, I wouldn't call it a blooper. Directors such as Ford and Hawks often staged a scene in which only some of the actors would have their lines, and the others would have to react and improvise. That gives a scene a freshness. If a trooper shoots a rifle and distracts Maureen O'Hara, for instance. If Wayne wanted the finale of the Green Berets with a dramatic sundown, I'm sure he knew it was geographically false. But here's one you'll enjoy - as a mistake. Spoilers ahead! Once you've read this, you'll always be looking at this scene differently.
You've been warned...!
Still here...?
OK. This is from Hatari!
In the very first rhino scene, behind the windshields of Pocket's car, you'll spot DALLAS in one single shot! Although she isn't even in the film yet - obviously some stock footage they used because it fit just right into the cutting of this particular scene. And that's what I mean: I'm sure they noticed that when they put it together. But because the scene is edited just right this way, and that shot is really short, they must've said: Nobody's ever going to notice. They didn't know about freeze-frame and VCR back then.