Revealing mistake: When Roy's in the ambulance with the man who was rescued from under The Boat, he's on the Biophone with Rampart, and just after Roy says, "So we've occluded the arterial flow in the right arm," in the next shot from inside the ambulance, we can see that they pass a couple of parked GlamourTrams. The ambulance drives around Universal's lot while shooting the footage inside the moving ambulance, en route to Rampart.
Revealing mistake: When John is in the moving ambulance with the pregnant gunshot victim, Brackett asks him if he hears fetal heart tones, and when John removes the stethoscope from his ears he leans back and we can see out the window that the ambulance is quite stationery, despite the siren.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy