I'll Fix It - S4-E2
Deliberate mistake: After Roy and Johnny rescue the man trapped under his house, when the ambulance reaches Rampart, in the shot from inside the ambulance when Roy follows the stretcher out, he stops at the receiving doors and waits for John, who just arrived in the squad, and in this semi-closeup, it's odd and very apparent that it's not actually Randolph Mantooth, it's his double meeting Roy at the door.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy