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There was an interesting Horizon programme on last night about committing the perfect murder. It largely covered old ground but there was one remarkable scene in it.

In fiction it has often been mooted that a block of ice could be used as a murder weapon. The idea is the ice eventually melts, thus destroying evidence. The programme decided to test this idea out. They had two forensic experts who doubted that it would work. A weapon was fashioned out of ice; it looked like a dumbbell with a spike on one end, and a couple of pieces of meat were readied for the experiment. The experts surmised the ice would shatter before it could do any damage. One of the experts struck the first blow to a thick piece of meat. It penetrated straight through the meat and hit the table beneath. He struck a second piece of meat – a section of rib this time – with the same implement and again the ice delivered a killing blow. The look of surprise on the faces of the ‘experts’ was priceless. Not only had the ice not shattered but even after two killing strikes it looked capable of delivering several more.

I give a speech about assumptions and this example demonstrates a key point perfectly. The experts assumed the ice would shatter. These were experts on human anatomy and biology. They were not structural engineers with a speciality in frozen liquids but they allowed their expertise in one field to cloud their judgement in another.

To be fair, they did challenge their assumptions (or at least the programme makers forced them to) and so discovered their error. This is how a lot of significant discoveries are made; an ‘outsider’ challenges the accepted wisdom of the experts and tests it through experimentation.

Making assumptions and guessing is not good enough; science demands that the demonstration is carried out and results analysed. And lo and behold we see what actually happens.

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