McGarrett, while undercover in jail with Barca, has the same inmate number (18790) as Barca does.
When the car is hauled out of the water, the trunk and the x-ray equipment in it are completely dry.
This episode opens with a high speed police pursuit in a fairly remote area, which was filmed either late in the afternoon or early in the morning. During one shot of the speeding vehicles shot from a distance, the silhouette of the film crew can clearly be seen on the low-angle shadows cast on the road where the vehicles are being driven.