Continuity mistake: Oliver chops off Malcolm's hand to end their duel. When Oliver hands the ring over to Nyssa you can see Malcolm lying in the background where he has been cut down with two hands intact, and the cut off hand nowhere in sight.
Blood Debts - S4-E10
Continuity mistake: When Conklin is whipping Oliver during an island flashback, the wounds from the whipping are visible, but after Oliver threatens to shoot himself unless Taiana remains unharmed he hands the gun to Reiter, and we get a good look at Oliver's back, wound-free.
Suggested correction: When Diggle is walking away from Felicity, he is still talking to her but it looks like he is talking to Nyssa.
Stephen Edmonds 1
People have already tried to correct this mistake. It is valid. In the scenes prior, Nyssa says Oliver will do what it takes to kill her and Oliver says "tonight, Nyssa Al Ghul faces justice." Nyssa is there to bring the team the news that Oliver is going to try to kill her. Felicity says "Oliver wouldn't", meaning Oliver wouldn't try to kill Nyssa. Diggle says "I think what she's [she being Felicity] trying to say to say is that Oliver would never do anything to hurt you" [you being Nyssa whom Oliver is going to try to kill]. He is meant to say "Nyssa." Otherwise the entire line means Nyssa or Laurel are there to convince Felicity that Oliver would never do anything to hurt Felicity.
Bishop73