When Frank is looking at the airline's flight passenger manifest, a close-up of the names shows that they are all character names from previous episodes. The most obvious one is "Mr. Curt Stoner" who was the police assassin in the famous "Hookman" episode.
During his telephone conversation with McGarrett about the court case Danno is munching a hot dog, which seems to be the meal of choice for Five-O staff this season. When they are discussing the case in a previous show this season, "Hara-Kiri: Murder", Danno, Chin and Ben are all eating hot dogs.