Well this is clever.
Appropriately-named Reddit user TooSkilled has edited together the Enchantment Under the Sea high school dance scenes from the first two Back to the Future movies, to create a single real-time clip.
It demonstrates just how much effort went into ensuring that the two visits to the dance matched up with each other to make the stories coherent - and all this in the days before digital technology, making the task a tricky one. Having said that, it's still taken a little movement from the editor to make it flow smoothly.
Check out the 17 minutes above, as Doc Brown, Marty, Lorraine and George McFly all attempt to save their futures, with another Marty trying to get back that sports almanac.
TooSkilled answered a few questions on the original Reddit post too: