Swimmers who jump into open water often die in their first gasp as they are hit by "cold shock" - the involuntary breath caused by cold shock can make you inhale too much water in seconds. You don’t even need to be underwater, a wave crashing over your face can cause a person to suck in as much as two to three litres of water - an adult can drown in just one-and-a-half. The reaction to going into cold water was coined as ‘cold shock’ by the UK’s leading expert on extreme environments, Professor