In recent years we've realised quite how bad a knock on the head can be for us, because the brain bobs about suspended in fluid inside our skulls. And if you move, or stop, the head suddenly, the brain cannons into the inside of the skull and can be injured. It's especially important in sports, but it's hard to study - and to develop effective safety equipment - for obvious reasons. But scientists have now discovered that something you commonly find in fridge door behaves in an uncannily similar way to your brain. Adam Murphy found out more... Like this podcast? Please help us by supporting the Naked Scientists