Deliberate mistake: During the mob scene outside Saito's love nest, the same black Saab is seen getting firebombed twice. It was shot from two different angles, with the two shots played about a minute apart to give the impression of two cars getting bombed. Also, in the first angle it is clear the car has no engine.
Deliberate mistake: The exact same filmed footage of sleeping Arthur is shown in two different scenes inside the van. This repeated slow-motion scene shows his left hand rising and two spherical droplets of water drift towards his right eye. It can be first seen when the van is being chased out of an alley and makes a right turn onto a street. Then it can be seen again soon after the motorcycle rider smashes into the windscreen. Watch for it when the van passes through open gates and makes a right turn. (01:29:30 - 01:38:55)
Chosen answer: The details are never explained in the depth, but all the dreamers are connected via the briefcase, so it seems likely that the briefcase acts in some way as a networking hub for them to share the dreamspace.
Tailkinker ★