Concrete which has apparently been sitting in a mixer for hours is poured into the victims car. Concrete is a mixture of cement, sand and gravel. Cement hardens by a chemical reaction not by air drying as is mistakenly thought by most people. Cement begins to harden as soon as it is mixed with water so it cannot be left in a mixer for hours.
The vet said he was raising Irukandji jellyfish to find a better way to put down horses. He pointed to a glowing blue thing about 5 cm across. They are red, about the size of a cocktail onion. Further, dying by Irukandji poison is about the most painful way imaginable to die.
An SUV is halfway filled with concrete, which would weigh several tons, and yet neither the suspension nor the tires show any sign of the vehicle holding such weight, showing that the concrete 'filling' the SUV is really just a thin layer on top of plywood or a similar material.
A thick black electrical cable is seen on the floor of Swanscombe House, running through a doorway, along a baseboard, and across a stairway landing, visible just to the left of DCI Tom Barnaby as Liz Gerrard introduces herself to him (at around 4 mins). It appears that someone took great pains to try to make the cable as inconspicuous as possible.
After finding incriminating items in the first murder victim's garage, Barnaby remarks that she may not have been the burglar, but could well be the vandal. No mention of any burglaries has been made up till this point. Apparently there were several burglaries which tied together various characters, but only one burglary was actually included in the story.