When Castle is in his office talking to his mother, you can see the gadget Doyle left behind sitting on a stand on Castle's desk. When the camera angle changes, the gadget is no longer on the stand but on the desk next to the stand. The next time the gadget comes into frame it is back on the stand. Nobody made any action to move the gadget at any time.
During crucifixion, nails are driven through the wrists and ankles, not the hands and feet. Since this is a common misconception, it's possible the error was made by the killer.
The actor tells Castle that the swords in the duel were props and could not hurt anyone. The foley work during the duel indicates the weapons are made of heavy steel which could hurt someone even if they were blunted.