In order to deflect suspicion away from Marni, Savage has his henchman administer a nasty beating to Marni at her store, resulting in severe facial bruises, but they fade away quite fast prior to the end of the show.
At the end Marni Howard was wearing a reversible scarf turned to the white side while she was inside her house, yet turned to the red side when she was in custody and led out the front door. It seems unlikely she would be concerned with reversing her scarf at the time of arrest or that the arresting officer would stand idly by while she reversed it.
Steve reveals to Marni that his middle name is Aloysius. However, in the earlier episode "Death is a Company Policy", Steve's name is given as Steven J. McGarrett.
The name on the mailbox of Savage's house was Carlisle.
When McGarrett and Dano race to the hospital to see about Ms. Howard: as the car makes a high speed U-turn, the front right hubcap is missing. And, there are already skid marks on the pavement. This is from the stunt driver practicing the turn.
When the newscast was showing on the TV after/about the bombing of McGarrett's office, there was no channel number lit up on the TV.
When McGarrett is visiting Marni in the hospital, Savage calls him to taunt him about what happens when an extortion victim cooperates with the authorities. But how could Savage know that McGarrett is there at that precise time. If McGarrett was followed, there was no evidence of that shown.
Wardrobe Department: Detective Frank Kamana meets his informer on two different days. He wears the same outfit both times, so does the informer.