(at around 5 mins) "Danno" is walking with his sidearm holstered and there is no magazine in it and then (at around 17 mins) the magazine is shown inserted.
In the scene where Dawkins is fleeing in the car after shooting Craig at the bank, we see him driving toward the airport early in the morning. The scene briefly flashes back to Dawkins in the car. When the camera turns back to the road, it's obvious that Dawkins is suddenly on a completely different stretch of road much later in the day.
When Catherine takes McGarrett's call, the hand that picks up the phone on the close-up shot is clearly a man's hand.
Prison/nails do not allow guns inside the facility. Guards certainly don't carry firearms.