Revealing mistake: At the funeral when Derek is giving the eulogy a tombstone on the right of screen almost falls over in the wind. (00:15:55)
Revealing mistake: When the projector screen gets rolled up, the picture of the Prime Minister rolls with it. It's painted on, not projected. (00:01:00)
Revealing mistake: In the scene where they confirm it's a walk-off between Hansel and Derek, Billy Zane is shown next to Derek saying stuff to stop him and Derek says: "put a cork in it Zane." Billy mouths those exact words and then tries to hide it.
Answer: It was raining and it was that water from before just running down the semi-sloped road.