Ko'olauloa - S1-E6
Continuity mistake: At the end of the episode, the surfers are in the bay to spread Ian's ashes. Ben lets go of Kono's hand and is handed the urn with the ashes by the man to his right. He removes the lid of the urn and hands only the lid back. Yet in the overhead shot immediately following, the urn is back on the board of the man to Ben's right, and there is nothing on Ben's board. He's holding Kono's hand again. In the next shot, he is tipping the ashes from the urn.
Ko'olauloa - S1-E6
Continuity mistake: When McGarrett chases the bad guys' Jeep, his Camaro skids through several huge dust clouds. Immediately after each cloud, however, the car is perfectly clean again. This is visible in several of the very rapid shots throughout the chase. After the chase ends, a coating of dirt and mud (which, incidentally, differs from the earlier shots) appears on the Camaro.
Chosen answer: They are Junior's SEAL buddies.