Revealing: In the episode when ACO Bulstrode is looking at the newspaper cut-out of the appliance crash (the one that Bayleaf was involved in), look closely at the cut-out. The whole article is just the same 3 or 4 lines repeating over and over again. Seemed the producers were too lazy to write a full article, hoping no-one would notice.

Revealing: In the episode when the schizo falls off the crane, the car he falls on explodes a split second before he actually lands on it.

Deliberate "mistake": Series 4 Episode 3. Before the gas explodes in the sewer, you can see the base of the Davy lamp glow red. Except that in real life this doesn't happen; the flame simply turns blue and grows taller in the presence of gas. This was probably done to make the scene more dramatic, though.

Revealing: Series 6 Episode 3. Just before the runaway car crashes through the car park wall, you can see the pre-cut area where it crashes through.