Hey kiddo, do you remember when we watched that movie where the hero was looking for a hidden treasure, but there was also a bad guy who wanted something else, and somehow both things were supposed to be important? That's what we call a double McGuffin!
A McGuffin is basically an object or goal that drives the story forward, while having no real meaning or importance to the overall plot. It's something that everyone in the movie cares about, but really, it's only there to keep things exciting.
A double McGuffin is when there are two of these objects or goals that are equally important, and they both drive the story forward. Think of it like two keys that fit into the same lock - both are needed to open the big treasure chest.
Sometimes, movies use a double McGuffin because it's a way to keep the audience's attention. If there was only one object that everyone was chasing after, then the story might become predictable: the good guys will get it, the bad guys will fail, end of story. But, if there are two objects, then the audience doesn't know which one is really important.
So, a double McGuffin is basically a way to make a story more exciting and unpredictable by having two important objects or goals that everyone is chasing after.