In "Hau'oli La Ho'omoaika'i" (Season 4's Thanksgiving episode), the plot revolves around a secret service agent that's killed while scouting for the president's upcoming trip to Hawai'i. A random trip to Hawai'i when the president would usually be in D.C. for the holidays seems out of place, until you remember that it's Barack Obama's birthplace. It makes the perfect cover for the real reason why he's meant to be there.
In Ka Noeʻau as a Brick Joke. It starts off with a man getting killed, said man is a hitman, killed by a hitman. It turns out the first hitman was sent to kill the second hitman and... people the second hitman didn't manage to kill that he sent to a safe place. The reason he didn't manage to kill those people mercilessly as he had done in the past was because he got ill, and had a heart transplant. This was the heart of a nice man, and suddenly he couldn't pull the trigger. So one could say that the hitman had a 'change of heart'.
When McGarrett dreamed he was his own grandfather, a police detective in 1941, his investigation into a teenage girl's disappearance is cut short by air raid sirens and fighter planes flying overhead. He immediately deduces that Pearl Harbor is being attacked. How does he know this so quickly? Because this is a dream of someone to whom the attack on Pearl Harbor is well-known history.
In "O ka Pili'Ohana ka 'Oi", why didn't Samantha escape 2 minutes after being left alone? She was locked in a dog cage, which isn't meant to contain humans, who could easily kick one apart from the inside.
