Revealing: In the opening scene when we see Jack and Victor as small boys and then turning into old men, look at Victor when he is a small boy. At one point he looks at the crew. It is over in a split second. Blink and you will miss it.

Revealing: When Jack and Victor are betting on whether a man slips on the ice or not, the man doesn't really slip but actually just jumps and lands on his back. This is extremely obvious when played in slow motion.

Other: In the inside of the flat where Jack and Victor dine with Frank McCallum, on the left wall there is a window on the left and a door on the right. However, this is impossible in their block of flats as we see in the exterior shots - there are no balconies and the layout of the building makes it impossible for a door and an exterior window to be on the same wall. From the cast commentary.