Do you have a dodgy ticker? Then you'll maybe want to skip the charity fundraising fad that is the Ice Bucket Challenge and jump straight to the part where you donate the money -- dousing yourself in icy water does some unexpected things to your heart.
As YouTube fact-master Tom Scott demonstrates, rather than getting the heart pumping faster with the adrenaline rush, the ice cold dunking instead triggers an effect called the Mammalian Diving Reflex. Cold water hitting your face leads the body to direct blood from your extremities back to your heart -- an evolutionary self defence mechanism to protect the organ, as the body doesn't know quite how long it's going to have to face the extreme temperature. If you've got a pacemaker installed, the Ice Bucket Challenge may therefore not be for you. [YouTube]