Think of the last time you went swimming. It is summertime at the lake; the little fishes are nibbling your toes and your brother is leisurely floating next to you. The cool, fresh water, having descended from the untouched purity of the frozen Canadian mountain peaks, is your oasis from the summer heat. You are playfully splashing in the shallows, and maybe your brother challenges you to a game every kid knows, and every fretful parent fears: the who-can-hold-their-breath-the-longest. Ready? You both count down together; three, two, one, you take a deeeeep breath, and under you go. You decide to…